''152i£^&os.rHCHa,.c.

Workshop onlU ?0985836

^

la^fe ' ^^S-PUS-C 1977

^^^^ NBS SPECIAL PUBLICATION 482

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

I

Rare Event/Accident

Research Methodology
I

NATIONAL BUREAU OF STANDARDS

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i
JU.N 3 0 1977

Rare Event/Accident Research Methodology

held at the National Bureau of Standards

Gaithersburg, Maryland, May 26-28, 1976

Edited by

V. J. Pezoldt

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

/u6 NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Proceedings of a Workshop

Issued July 1977
Library of Congress Cataloging in Publication Data

Main entry under title: Rare event. (NBS special publication ; 482)

Sponsored by the Human Factors Section of the Center for Consumer Product Technology.

Supt. of Docs. no. C13. 10:482

1. Product safety—Research—Congresses. 2. Accidents—Research—Congresses. I. Pezoldt, Val. II. Center for Consumer Product

Technology. Human Factors Section. III. Series: United States. National Bureau of Standards. Special publication ; 482. QC100.U57 no. 482 [TS175] 658.5'6 77-608110

National Bureau of Standards Special Publication 482

Nat. Bur. Stand. (U.S.), Spec. Publ. 482, 112 pages (July 1977)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office, Wasnington, D.C. 20402

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(Add 25 percent additional for other than U.S. mailing).
TABLE OF CONTENTS

Page

Acknowledgements v

Abstract vi

Introduction vii

Papers Presented at the Workshop

System Safety Engineering as the Integrator of Accident

Prevention Activities

Willie Hammer 1

Investigative Methods Useful in Safety

W. G. Johnson, presented by Robert Eicher 11

Hypothesis Generation for Rare Events Research

Ludwig A. Benner, Jr 25

Epidemiologic Approaches to Injury Research

Julian A. Waller, M.D. , M.P.H 29

Needed Human Research and New Methodological Considerations

Being Forced by the Law

George A. Peters, Esq 47

Methods for Studying Complex Homemaking Tasks

Rose E. Steidl, Ph.D 55

Data Collection for Hand Tool Injury: An Approach

M. M. Ayoub, Ph.D., P.E 71

Simulation in Accident Research

Stanley Rubinsky, Ph.D. , P.E 105

Participants in the Workshop Ill

iii

ACKNOWLEDGEMENTS

The editor wishes to thank the participants in the Workshop on Rare

Event/Accident Research Methodology and especially the authors of the papers

contained in this volume who gave freely of their time and wisdom to

make the workshop a thought provoking^ learning experience for all who

attended

.

Thanks are also due to Kim Howard for secretarial assistance both in

the preparation of this document and during the workshop.

v
i ABSTRACT

This volume contains the formal papers presented at j a Workshop on Rare Event/Accident Research Methodology

sponsored by the Human Factors Section o£ the Center for

Consumer Product Technology, National Bureau of Standards

held at NBS May 26-28, 1976. The topics addressed at the

, workshop and reflected in the papers in this volume include system safety engineering, hypothesis generation

in accident research, epidemiological approaches to injury research, observational techniques for studying complex tasks, accident simulation, and methodological con-

| siderations being forced by the law.

I

Key Words: Accident research; human factors; methodology;

rare events; safety; system safety.

vi
Introduction

The National Bureau of Standards (NBS) has long been involved in

research and standards development activities in the areas of product

performance and product safety. The Bureau's commitment to these

activities was increased when, in 1974, the Institute for Applied Technology

established the Center for Consumer Product Technology (CCPT) . The Center's

mission is:

to perform research and development toward establishing

and advancing measurement techniques and test methodology

necessary to evaluate safety and other perfomance

characteristics of consumer products.

In support of this mission, the Human Factors Section, a unit of the

Product Systems Analysis Division within CCPT, sponsored a Workshop on

Rare Event/Accident Research Methodology. The purpose of the workshop

was twofold: (1) to further familiarize Section staff with a variety of

methods currently being applied to safety problens, thereby improving the

Section's capabilities; and (2) to provide a forum for the exchange of

information and ideas among a small group of safety practitioners and

accident researchers.

The workshop was held at the National Bureau of Standards' Gaithersburg

,

Nb-ryland facility May 26-28, 1976. Eight invited participants from outside

NBS made presentations to the workshop and acted as discussants in sessions

devoted to their particular specialities . This volume includes the papers

prepared by each of the eight presenters which served as the basis for

their presentations to the workshop. A broad range of topics pertinent

to rare event, safety, and accident research were presented. The topics

addressed at the workshop, and reflected in the papers here, included

systems safety engineering, hypothesis generation in accident research,

epidemiological approaches to injury research, observational techniques for

studying complex tasks, accident simulation, and methodological considerations

being forced by the law.

vii

SYSTEM SAFETY ENGINEERING AS THE INTEGRATOR

OF ACCIDENT PREVENTION ACTIVITIES

Willie Hammer

Hughes Aircraft Company

WILLIE HAMMER has held a wide variety

o£ engineering positions. Since 1961 he

has been involved entirely in safety engineering,

with the Air Force, a consulting engineering

firm, and now Hughes Aircraft Company. Mr.

Hammer has taught product and systems safety

courses at UCLA, the University of Wisconsin

and abroad. In addition to numerous published

articles on various subjects, mostly safety.

Hammer has written the highly regarded Handbook

of System and Product Safety (Prentice Hall,

1972) , and Occupational Safety Management Engineering

(Prentice Hall, 1975)

.

Hammer's workshop presentation provides

an overview of the discipline of System Safety

Engineering and a brief review of the philosophy

and methods of System Safety. Central to his

discussion is the principle that accident prevention

activities involving any product or system must

be initiated with the earliest concept of that

product or system and be maintained throughout

its life cycle. As suggested in the title of

his paper. Hammer considers this discipline

a prime candidate for the task of integrating

the contributions of many specialities into

a comprehensive program of accident prevention.

The analytic methods of System Safety, as presented

by Hammer, provide a logical framework for applying

the results of research and experience to the

very real safety problems faced by industry.

Accident prevention is an activity involving many considerations,

managerial activities, and technical disciplines. This workshop was called

because of this and to familiarize each participant with the areas of

interest, methodologies, and capabilities of the other participants.

I am a system safety engineer. For those of you who are not familiar with

system safety engineering, some background information may be of interest.

After World War II, personnel concerned with prevention of aircraft

accidents began to express their view that safety must be designed into

airplanes like any other required characteristic. Some aircraft companies

formed safety organizations to this end, but it was not a concerted effort

throughout industry.

1
The concerted effort began in the early 1960 's because of Air Force

concern for safety with highly lethal intercontinental ballistic missiles.

The missiles were capable of causing horrendous injury and damage. If one

was lost catastrophically no blame could be put on a pilot, as in an aircraft

accident, since there was none on board a missile. In addition. Air Force

operating units were being given vehicles powered by exotic fuels and oxidizers

with highly dangerous characteristics. The philosophy developed that safety

programs had to be initiated almost as soon as the new system was conceived,

and carried on through all phases of development, production, and operation.

To mitigate seme of these problems requirements were written into

contracts which required safety efforts to be undertaken during development of

missiles. These requirements were generally limited to those contracts

for which there was serious concern for safety, and for which someone in

authority was knowledgeable and forceful enough to have them imposed. In

1962 work was initiated on an Air Force specification which would require

all missile contractors to undertake system safety programs. This was soon

extended to aircraft and other Air Force equipment. The concept was soon

caught up by the Army (especially for helicopters) and the Navy so that the

Department of Defense issued directives requiring system safety programs be

undertaken for systems to be developed or modified. Six years ago, perhaps

one of ten contracts for military systems had requirements for a system safety

program; now the rate is about eight of ten.

System safety programs were being called for but there was a lack of

methodologies for accident prevention which could be used for complex systems.

There is no school, technical society, or other large organization at

which research in system safety engineering is being conducted. Therefore,

we who work in this discipline must sometimes do our own research in order to

meet the requirements of our jobs. We have adopted, adapted, and developed

methods. We have been forced by necessity into an organized approach to

accident prevention by:

. Evolving new concepts and methodologies.

. Refining old concepts and methodologies

.

. Adapting techniques from other scientific, technical, and

management disciplines to our needs

.

. Eliminating erroneous, invalid, or unnecessary data,

concepts , requirements , methods , or equipment

.

Integrating related management and technical

activities

.

Programmed, systematic determination of hazards and

their elimination or control.

To accomplish our jobs we had to know something about program management,

and about the activities of other engineering disciplines, their objectives,

techniques, and capabilities. There are many disciplines whose practitioners

2
were (and are) concerned with safety and accident prevention but who were almost

always also interested in additional considerations. System Safety and reliability engineers share a concern regarding malfunctions which could lead

to accidents. If a malfunction cannot cause an accident, we safety engineers

are not concerned. Reliability engineers are interested in any malfunctions

and in quality control of all operable items. Maintainability engineers

are interested in malfunctions which require repair; they are also concerned

with logistic support of a system or product. System Safety engineers are

concerned with maintainability engineering for two reasons : the lack or

inadequacy of which could result in accidents to operators, and in designs

which could cause injury to maintenance personnel.

We in System Safety engineering believe that a hazardous condition must

exist in order to have an accident. These hazardous conditions can be due to

personnel errors, mechanical failures, dangerous characteristics of

equipment or material , and/or adverse environmental factors . There are

numerous instances in which these overlap. For example, hazardous

characteristics of equipment or material are either inherent or created by

design error, one of the subcategories of personnel error. I have put the

four categories and their interrelationships into a mathematical

expression (Exhibit 1) to indicate simply the various factors involved.

Some of the engineering disciplines, besides System Safety, which might

be interested in the four rough categories would include, but not be limited

to:

. Personnel errors: human factors engineers, psychologists,

design engineers, and procedures and manual writers.

. Mechanical failures: design engineerings, reliability engineers,

metallurgists, quality control engineers;

. Hazardous equipment or material: design engineerings, chemists

and chanical engineers, materials engineers, industrial hygienists,

biochemists

;

. Environmental factors : design engineers , meteorologists , industrial

hygienists, structural engineers, sound engineers.

Note the fact that design engineers are cited in each case. An

objective study would undoubtedly reveal that many injuries and much damage

could have been, and can be, avoided by better designed equipment. Safeguards against accidents should be designed into equipment as much as

possible, and little reliance placed on procedures to be followed by users.

I said there is no school at which research in system safety engineering is

being conducted. The situation is only slightly better when it comes to

teaching system safety engineering to undergraduate engineers . The courses in

existence teach safety engineering to students aiming to be safety engineers,

but unless they have been instituted very recently, I don't believe there is a

school which teaches safety to engineers who will go into other fields,

especially design. Yet, these are the ones who will be designing the equipment

which turns out to be unsafe.
What have we System Safety engineers done so far which could be considered

noteworthy?

. This discipline is predicated on the principle that

accident prevention activities involving a system or product must begin with

the initial concept of that system or product and be maintained throughout

its life cycle. Tasks have been developed to be carried out during each phase

of the life cycle. The erroneous idea that safety engineering during

development before a product is unnecessary before it is built and tested

must be eradicated. A list of safety tasks, the outputs and potential

problems in carrying out a product safety program are presented in Exhibit 2.

. One of the first and most important tasks listed in

Exhibit 2 is the preparation of safe design criteria to be observed by

designers. Good standards for safe design must be provided as soon as the

system or product is conceived. There must be means for ensuring that the

standards are observed. But even with the best standards, hazards can still

exist in a product. There must therefore be means for analyzing the

system or product to make certain that these potential hazards have been

eliminated or controlled.

Safety criteria in most product standards are generally

lacking, inadequate, or ineffective. The A. N.S.I, standards for products

are not only wanting in respect to safety, but because they are voluntary

are often ignored. Admiral Hyman Rickover's comments regarding standards are

noteworthy:

"To forestall intrusion of Government, the industry concerned

will usually propose voluntary safety requirements . These requirements

represent the minimum all are willing to accept. This is not enough. There

are more accidents . Only after the lapse of much time are laws finally

enacted. Mach harm will have been done in the interval --harm which could

have been prevented.

The typical industry- controlled code or standard is formulated

by a committee elected or appointed by a technical society or similar

group. Many of the committee monbers are drawn from the manufacturers to

whom the code is to be applied. Others are drawn from engineering consulting

firms and various Government organizations. However, since near unanimous

agreement in the committee must generally be obtained to set requirenents or to

change them, the code represents a minimum level of requirements that is

acceptable to industry.

In a subtle way, the use of industry codes or standards tends to

create a false sense of security. Described by code committees and by

the language of many of the codes themselves as safety rules , they tend

to inhibit those legally responsible for protecting the public from taking

the necessary action to safeguard health and well-being. Nfeny States

and municipalities have incorporated these codes into their laws, thus,

in effect delegating to code committees their own responsibility for protecting

the public."

4
If we conpare safe criteria stipulated in industry standards with

those in government -prepared documents, such ^s in military specifications

and standards , we find the government criteria more stringent for the

same hazards. In addition, they are wider in scope. Yet these military

requirements are for personnel whose mental and performance capabilities

and training are far higher than the general public who are to be protected

by industry standards. If the Consumer Product Safety Commission has

industry develop its own standards, as it has been attenpting to do,

it will recreate the same unhappy situation Admiral Rickover has described.

One possible solution is the use of a new system which at Hughes

Aircraft Company have recently developed and are still refining. We

call it SCRAT, for Safety Criteria Retrieving and Tabulating. It is

predicated on the idea that any system, product, subassembly, or material

can have only certain hazards and that the safe design criteria for these

hazards can be prepared to apply in general terms to all items which

have potential hazards. We have, therefore, put safe design criteria

for our products into a computer. When we want the criteria for any

item, we can retrieve them at will for the specific design being undertaken.

A safety engineer then reviews it and adds any other safe requirements

that may have been stipulated for observance in a contract. We are still

refining the system but even the early usages we have been beneficial.

The process could be expanded for use by the Consumer Product Safety

Commission to satisfy most of its needs for developing product safety

standards . (The criteria we use are for the products we produce and

limited in scope. In addition, our criteria are derived from military

specifications and standards.) The computer readout can also be used i by C.P.S. engineers as checklists to evaluate whether a product appears

to be safe.

There are numerous other uses to which SCRAT can be put. If any

of you are interested and want further information, please let me know.

The "Fly-Fix-Fly" methodology of determining potential hazards

which might exist in a product only by reviewing the causes of

'

accidents or presentations in lawsuits cannot be justified logically,

economically, operationally, or morally. To determine and control the

potential hazards which could exist in a system, product or operation,

new methods of analysis have been developed. The best of these. Fault

Tree Analysis, was originated by Bell Telephone Laboratories under an i Air Force contract. The Air Force was much concerned that the Minuteman

ICBM could be launched or the nuclear warhead detonated either inadvertently

or by an unstable person. A means for assessing the possibilities qualitatively

and quantitatively were wanted. The techniques of reliability analysis

were inadequate for the purpose: the effects of multiple failures were

not considered; personnel error and other actions were not considered;

possibilities of single point failures could not be established.

For those who are not familiar with Fault Tree Analysis, a very

brief description may be in order. A specific adverse event or condition

to be investigated is selected. All the factors which can contribute

directly to this event or condition are then shown on a logic diagram. The causes

5
of these secondary factors are then added, developing downward like the

roots (although they are called branches) of a tree. Following the tree

downward indicates the causes of an event; following it upward indicates

the effects.

The Fault Tree can be used for qualitative purposes to indicate

diagrammatically the cause and effect relationships , or it can be prepared

so that probabilities of the top, specific adverse event can be calculated.

By means of Boolean algebra, mathematical equations can be written and

sinplified which will express the top event in terms of the basic causative

factors. Simplification of the equation will eliminate redundancies.

In addition to providing an expression for the top event, the simplification

will indicate where potential single point failures exist. Probabilities

of occurrence of the basic causative factors can be inserted in the equation

and the probability of the top adverse event calculated.

Because it was the prime contractor for the Minuteman system, the

Boeing Company became the first major user and proponent of Fault Tree

Analysis. Bell Telephone Laboratories personnel had indicated symbology

to be used; Boeing personnel added to it. (Symbols generally used are

indicated in Exhibit 3; a simple Fault Tree in Exhibit 4.) There are

many variations in symbology, generally to simplify usage. Notation are

used to permit computer calculation and preparation of fault tree diagrams

for complex systems

.

The method is being used for purposes other than safety. Reliability

engineers are using it. The top event selected is one indicating that

successful accomplishment of an event (only material failures are included)

.

The probability of successful accomplishment is, by definition, reliability.

Other applications of Fault Tree Analysis have been in accident investigation, where the top event is the injury or damage which occurred. IVbnagement

Oversight and Risk Tree (NDRT) , developed by Aerojet Nuclear Company,

endeavors to establish logically the contributory management events which

could or fail to produce a specific management objective.

Fault Tree Analysis is an excellent method but is not usable for

all accident prevention analyses. Its basic premise is analysis of a

specific event. Factors which do not contribute to that event are not

included in that tree. If they are to be considered, another tree with

a suitable top event must be developed. The lower levels of the tree

frequently cannot be developed until after the product is designed. System

Safety engineers, therefore, use other types of analysis, from simple

analytical reports to more complex mathematical studies. For example,

at the beginning of a development program a Preliminary Hazard Analysis

if usually prepared which provides an initial assessment of hazard which

would be present in a new product or operation as proposed. Corrective

action could be taken immediately.

6
. Another area in which we have been working is in quantitative

measures of safety. I pointed out that the inadequacy of reliability

methodologies to this end was a compelling reason the Air Force went to

Bell Telephone Laboratories, leading to the development of Fault Tree

Analysis. There are other reasons for interest in quantitative measures:

+ Risk assessment. Many companies would like to know the risk which

use of certain equipment or conduct of certain operations would entail.

Decisions can be made based on economic justifications determined this

way. Insurance companies are interested. To determine potential losses

it is necessary the probability of an accident or accidents be known.

It is frequently undesirable, especially with new products, to obtain

probability values from accident statistics

.

+ Establishment of acceptable safety levels. A regulatory agency,

such as the Consumer Product Safety Commission, can require that products

meet stipulated safety levels before they can be put on the market. The

British Civil Aviation Authority is already doing this with aircraft to

be certified for flights into the British Commonwealth.

+ Comparisons. Quantitative levels can be used to compare two or

more designs to see which is safer. Safety analysts in nuclear power

design activities have done this.

We have been running into problens in this area. Some of the solutions

will depend on activities in other disciplines. For example, we need

good, valid data on probabilities of human error. There have been abuses

in the use of quantitative goals , but little by little the problems are

being eliminated.

The philosophies of System Safety, the concept of life-cycle program

planning, and the techniques of SCRAT and of hazard analysis can be applied

universally in accident prevention. A good System Safety engineer will

be knowledgeable in all of these. He may not be as well qualified in

highly specialized disciplines from which it is necessary to obtain esoteric

information. Where data on probabilities of human error are required

he must step aside for the ]iuman factors engineer or the psychologist.

On the other hand. System Safety methodologies can be used to determine

how the efforts of specialists can best be utilized in an effective course

of action. System Safety engineering methodologies can be used to integrate

accident prevention programs

.

That, to a limited extent, is what we System Safety engineers do.

I hope that one of the outcomes of this Workshop will be a recommendation

for accident prevention research programs over a long term. I hope that

we System Safety engineers are invited to participate in the development

of the programs and in specific research activities. We have the people,

the methodologies, the capabilities, and the experience.

7

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9
10
INVESTIGATIVE METHODS USEFUL IN SAFETY

William G. Johnson

Energy Research and Development Administration

This paper was prepared by WILLIAM G. JOHNSON

and discussed at the workshop by ROBERT EICHER.

Mr. Eicher has worked closely with Johnson at

the Energy Research and Development Administration

(ERDA) (formerly AEG) where he is Special Hazards

Engineer in the Division of Safety, Standards,

and Compliance. Mr. Johnson, retired general

manager of the National Safety Council, is the

author of M3RT - The ^fanagement Oversight and

Risk Tree , which he prepared for the U.S. Atomic

Energy Commission, Division of Occupational

Safety.

MORT is a major output of ERDA's continuing

development of a safety management methodology

for reducing accident rates. Application of

M3RT has been primarily in occupational safety,

however, many of the techniques and methods

employed can be useful in consumer product technology

as well. The paper presented here serves, in

large part, to introduce and annotate MORT for

the workshop participants.

For the past six years ERDA (formerly AEG) has been developing a

safety management methodology to augment its basic physical research goals.

AEC had had safety programs and records equal to the best practices of

private industry and government. Nevertheless, the goal of the development

work was stated as "an order of magnitude reduction in rates and risks."

The investigative method used in the developing "superlative safety

assurance systems" for ERDA was as follows:

1. Conceptual framework -- development of a trial synthesis

from the best organizational practices, aerospace system safety

methods, safety related research, and behavioral, organizational

and managerial sciences;

2. Further development from analysis or reinvestigation of accidents;

3. Trial in an organization (Aerojet Nuclear), and then restatonent

of the synthesis ;

4. Application, training, and technical assistance agency-wide;

5. Ongoing development, especially at Aerojet, but also as numerous

laboratories and production facilities

.

11
The primary outputs have been two:

^ORT - The Management Oversight and Risk Tree , U. S. Atomic Energy

Commission, February 12, 1973, SAN 821-2.

Accident/Incident Investigation , Energy Research and Development

Administration, August 1, 1975, ERDA-76-20.

In progress is Workbook on Measurement of Safety Assurance Programs . A

review draft is scheduled for May and a pilot training draft for the Fall,

1976. The Workbook will offer numerous examples of the measurement data

believed needed, augmenting the hundreds of specific questions already

posed in NDRT. A method cumulating many specific measuronents into

assessment of eight broad system criteria will be proposed.

A growing number of supportive publications are coming from System

Safety Development Center at Aerojet:

Occupancy-Use Readiness Manual,

Human Factors in Design,

A Contractor Guide to Advance Preparation for Accident Investigation,

MDRT User's Manual (to be published shortly).

In addition a variety of training aids and experimental forms are

of interest as to methodology.

Organizational research in safety has the following obstacles:

1. The rarity of major events,

2. Difficulty of cross-context comparisons of complex organizations,

3. Paucity of basic research or relevant data,

4. Lack of research orientation among safety practitioners.

The synthesis has supplied a conceptual framework wherein investigation

becomes more searching and testing of control programs is more nearly

possible.

In the course of the six-year project a wide variety of research and

investigation methods have been assimilated , and some new methods have

been developed.

The three years subsequent to publication of MORT have included

widespread examination and use of the systems by managers and scientists

of many disciplines. The usage has confirmed the basic 1973 report, and

resulted in extension and development rather than drastic change.

A A ^:

12
The relevance o£ the "superlative safety systems" for consumer

product technology lies in two areas:

1. Product safety up to the point of consumer use is amenable to

the same control processes (given the substitution of appropriate

use and user data, consumer rather than employee)

;

2. Some elements of the system may have relevance or usefulness in the

consumer use phase, but because of the obvious differences between

controllable employee behavior and typical consumer behavior, the

use phase requires separate evaluation of any given study method for

a control or technique.

* * *

For the convenience of Workshop participants, a reprint on WRT from

the Journal of Safety Research, March 1975, is attached as Appendix A.

Also, ERDA has made available copies of the above publications to Workshop

participants

.

This paper could be called a "Smorgasbord of Investigative Methods."

The intent is to call out the developments within the project briefly. Then,

if the reader is interested, the texts or references can be consulted. Many

specific measurements and experiments are described in the text.

The order of listing, with a few exceptions, follows the order of the

MDRT text.

I. Introduction . Among other concepts, the significance of codes,

standards , and regulations is presented. They are minima. Useful and

necessary to put a floor under performance, but not the route to the

optimum performance desired by all.

II . What Procedures Hazards

1. Accident/Incident definition . An essentially new definition is

presented (p. 25) . It was developed for functional use in design

of safety measures. (Short definitions may be superior for

tabulating events, but do not lead into essential preventive

aspects.) Also Hazard and Risk are defined.

2. Energy and Barriers . The Gibson-Haddon concepts are simple and

objective, and have many advantages for prevention analysis.

Systematic, sequential analysis of possible barriers has repeatedly

produced innovative safety devices of superior efficacy.

3. Frequency- Severity Matrices . Different accident sources typically

have different slop lines . A slop less than the 45° line of

balance is a danger sign, and appears to have catastrophe prediction value.

13
4. Error as Accident Cause . The substantial literature on error

measurement and error reduction methods can be brought to bear

on safety.

a. Rigby's "error tolerance limits" (p. 52) useful in studying

degrees of control , provide macabre humor when a limit turns

out to be "forensic."

b. The Surry decision model (p. 54) has been under careful

observation. While it seems conceptually correct, its

practical significance seems limited under circumstances

of typically subtle danger buildup often conditioned by

changes remote in time, and the blinding speeds of

accident occurrence. If non- injury errors or unreviewed

changes were seen as danger signals, the Surry scheme could

be useful. (See McKie, p. 61, for a natural history note.)

c. The extensive reliability and error prevention work of ERDA's

weapon production program is essentially product safety. Mich

in the way of useful concepts and data on error -provocative

situations has emerged. A key point in the work of Sandia

Lab is the need for error rates of the general form: errors/

opportunities, i.e., the need for user data as well as accident

data.

5. The Role of Change in Accidents . This is one of the most important

MORT developments. The basic concept of Kepner-Tregoe--in a

stable system, change is the cause of the trouble--was initially

studied by NSC and has been under intensive study by ERDA. Change

analysis is a most powerful technique for identifying obscure

causes. It is particularly useful in product quality assurance.

(The form on page 67 is not a form to be filled out. The left hand tabs

are intended only to be indicative of the event-related factors to be

inserted.)

Most (perhaps all) serious accidents have one or more changes, usually

detectable.

Equally powerful as a preventive medium is "Change Based Potential

Problem Analysis." (The form on page 69, as now used, has a column "Effects

of Change" inserted before "Preventive Counter -Change.")

This analysis could be significant in design of a revised model of

a product. Call out all differences (e.g., as irrelevant as color), then

analyze Effects of Change. It often turns out that so-called irrelevant

changes have significance. This inexpensive, perceptive form of analysis

should be a requirement on every project and for every significant change.

The effects of changes are directional and exponential - -quite a

challenge!

14
6. Sequences in Accident Causation . MDRT (1973) is essentially just

descriptive of a phenomenon of lengthy sequences

.

The use of sequence as an analytic device was developed by

Benner and Wakeland for NTSB. Following their leadership the ERDA

Accident/Incident Investigation Manual (AIM), pages 4-3 to 4-8, and

Appendix I, discuss the method, "Events and Causal Factors Sequence

Diagram," and show illustrative cases. The sequence diagram is

the usual focal point of analysis.

Sequence diagrams, coded by MDRT codes, now seem a realistic

possibility for causal information coding and retrieval.

7. The Role of Risk Management . The scientific literature is summarized,

but provides little practical material. The concept which associates

risk with the profitable, creative, and "fun" side of a line of

balance is articulated. The simplest useful model of risk

assessment is described.

Ill . How to Reduce Hazards

8 . Integrating System Safety with Present Best Practices . System

safety, as developed in aerospace and nuclear industries , is

project related. Insofar as product safety is a project by

project effort, system safety can be a recommended approach. The

text provided by Willie Hammer* (a Workshop participant) is a

valuable guide.

The need to integrate system safety with the best organizational

practices arises from the ongoing, continuous operation of the

organization, not usually seen as merely as series of projects .

The MDRT synthesis incorporates system safety with numerous

references (Hammer's text was not then available). However,

by now MDRT also incorporates many methods and criteria not

customarily found in system safety, e.g., change analysis,

independent review, procedure criteria, the full spectrum of

human factors concerns, ongoing monitoring and audit systems,

and the basic management policy and implementation factor.

The basic position is that MDRT and project system safety

are noncompetitive. Start with whichever one seems appropriate

for an ongoing organization or a project and then add the other.

9. Method vs Content . Analytic or observational method (with good

people) ?ias repeatedly shown that it is Fast and Cheap , and that

it can find some deficiencies not usually revealed by hardware,

technical or process specialists. Examples again are error,

change, and sequence analysis.

*Hammer, Willie, Handbook of System and Product Safety , Prentice Hall, 1972.

15
10. Safety, Efficiency and Performance are Congruous . This tenet

can be illustrated with anecdotes and strong beliefs in some

business circles. It is not scientifically proven. This

carries over to consumer products which commonly have energy

use or conservation methods of performing work.

If organizational safety program is redefined as those

elements likely to improve safety and performance, the mutual

reinforcement is enhanced. Increased positive emphasis on safety

is then supported by management. Emphasis solely on codes,

standards and regulation will not suffice, nor does it tend to

build management support.

An inherent relation between energy, control, and

performance (p. 109) underlies much of what we undertake in

modem society. When control is not in scale, performance

suffers and accidents result.

11. A Safety System as a General Management System . We reinvent

nature's biological safety mechanism with essential feedback

as a "safety system," or a wide variety of managerial systems.

The beauty of the simple, six element system (p. 113) is that

under it we can tree (successive elaborations of essential detail)

everything that must be said about safety methodolgy. For example:

Simple - six elements - p. 113

Congruous with general

Next level of detail - p. 114 management - p. 128

More detail - M3RT

Note a tree is a sequence - left to right and top to bottom.

A tier in a tree is a process - p. 194.

Additional trees can give more detail, e.g.. Independent

Review tree. Exhibits 8 plus 4-7 and 9-12, or for other

subjects. Exhibits 3 and 12.

12. General Safety Program Theses . A simple set of propositions

reflects what has gone before and what will follow.

IV. MDRT . The appendix to this paper provides the necessary discussion.

If M)RT seems complex, remember that it must be "necessary and

sufficient," and also provide redundant controls.

V. Management Implementation of the Safety System. Ten elements

susceptible to measurement and evaluation are listed and described.

The e Lemer^ts are correct and basic if the product is a reactor, a

process facil "'"v, or a product used by others (industry or government)

with y. strong :em for safety.

16
The management criteria have not been tested on a consumer product

organization. Product safety specialists have opinions that the management

elements for product safety are similar, if not identical. A study of

product-related management systems could bring about major improvements

in product safety. This thesis will be repeated in the Hazard Analysis

part.

21. Risk Assessment System. Models varying from simple to complex are

presented. Probability goals for safety are now feasible and practical.

ERDA now has several active investigations in analyzing risks in

transportation of hazardous materials, using the NTSB model. This

model, converted to general organizational problems, is shown (p. 219).

VI. Hazard Analysis Process . The Hazard Analysis Process must be

conceptualized and defined. The failure to do so is probably the

most glaring single weakness in present-day professional safety work.

22. System Safety and Hazard Analysis . Two concepts. Life Cycle and

Safety Precedence Sequence, were well articulated by NASA (but not

AEC at the time)

.

System safety costs (perhaps 5% of engineering costs, and a tiny

fraction of total production costs) are essentially small . Managers

and engineers commonly see them as expensive; this has never been shown.

What can be expensive are the hardware or control systems shown

necessary by analyses ; then trade-off studies may be necessary and well

based.

23. Hazard Analysis Process Defined . The listing referred to on page 235

is "MDRT IV," an improvement over the M3RT charts in the text, but

similar to the large chart which accompanied the Safety Research

Journal (MDRT V)

.

The need for the elements in this process has been confirmed in

spilled blood and piles of rubbish and ashes. Lack of articulation

of such a process is the grave weakness in product and other design.

To facilitate initiation of an improved process, the

simplification shown as Figure 1 was developed. It shows the

"big six" of hazard analysis which will merit brief comment here:

a. Information search

(1) Codes, standards and regulations;

(2) Accident/ incident data. Without any desire to relieve

manufacturers, the difficult matter of nationwide product

data collection and retrieval may be a valuable service for

government action.

b. Change Analysis, already discussed.

17
c. Failure IVfode and Probability/Consequences analysis of residual

priority problem lists

.

d. Human Factors Review, covered in MDRT chapter 26. The MORT tree

analysis shown follows common practices, but has demonstrated no f efficacy in upgrading investigations or reviews by untrained

personnel. We fell back on a classification of skill levels, a

low threshold of a "cookbook" or a sensitizing course such as the

Aerojet manual cited at the outset. The skill applied to product

design is easily classifiable, and the threshold should be a

minimum requirement in modem society. Here standards for design

will not suffice.

e. MDRT analysis.

f. Nonnormal operating modes- -start up, shut down, repair, failure,

anomalies, etc. --search is a test of imagination.

The final level of required system safety analysis is negotiable

from a scaling mechanism- -big problems, big analysis- -and for a

major system safety effort. Hammer is, again, the best guide.

We can now return to some of the other major elements in Figure 1

Good Design Organization (Chapter 27) . Strangely, a general format

of a design process, onto which a safety process can be easily

fastened, is apparently lacking. The points of interactions,

particularly early safety input, should be defined.

The role of reliability and quality assurance are understated

in MDRT (1973), especially for product safety.

What is called for is a three-level investigation or audit of a

product design function:

a. Basic design organization.

b. Quality assurance aspects (p. 281).

c. Hazard analysis process (p. 235).

Only the three in combination could give assurance of an error

free design process.

Independent Review . This concept was apparently invented by the

AEC, and it is a powerful factor in detecting oversights and omissions

Trade-offs are not a functional point of design clearly

called out in MDRT. Safety is a frequent loser in trade-off sessions

because the predictive safety data for cost/benefit con5)arisons are

weak relative to other concerns. Therefore, the injuction to

always put in the values is made, which will be clear when serious

accidents occur (p. 256)

.

18
Historical Note . The automobile industry can under excrutiating

pain in Senate hearings in 1963 and 1964. Its management

policies and implementation, its safety research, its hazard analysis

process, and its trade-offs fstyle for safety) were found less than

adequate (LTA in JVDRT) . One company president has said he wishes

he knew prior to 1963 what he now knows. The lesson for other

manufacturers seems clear- -audit and measure processes against

ideals, or public agencies will.

VII. The Work Flow Process

Operational Readiness is a test not covered in M3RT, but not has the

Aerojet guidelines listed above. The process therein shows analytic trees

which, with slight adaptation, could be used to determine that a

manufacturer was ready to produce a safe, trouble-free product.

However, a simple guideline for universal use is the Nertney Wheel

Cp. 254).

With one exception. Procedures, the factors of Supervision, Employee

Training and Performance Motivation seem inappropriate for consumer

product technology.

Procedures (chapter 32) . Tested criteria for evaluating procedures

are listed. (Seven of ten procedures in a well-run organization flunked

the test.) It seems likely most manufacturers' procedures would show at

least as high a failure rate.

New View on a Human Factors Process . M3RT divides the human aspects

into several pieces, remotely classified as relevant to a MDRT process.

To tie it all together. Figure 2 was developed. The following numbered

notes explain the steps in the process. (Other steps are clear, or see

MDRT index.)

(1) Any number of tests and guides . See special bibliography in

^DRT.

(2) See Procedures above and IVDRT, Chapter 32.

(3) Behavior change - Appendix H, Innovation Diffusion, and

Appendix I, Acceptance of Proceduralized Systems.

(4) M^ger and Pipe, Analyzing Performance Problems , Lear Siegler, Inc.

Fearon Publishers, Belmont, California, 1970.

It should be most fruitful to measure the Human Factors Process as it

would bear on designers in an organization. They are people, and need

support and assistance.

VIII. Information Systems . The specific criteria listed 343 would

likely not be fulfilled by a product data system. Again, government

may have a role to fill. The manufacturer does have certain

inescapable obligations.

19
36. Technical Information . Can be well organized and approach comprehensive

change

.

37. Monitoring Systems . Some can be developed.

a. Error sampling is possible by field study.

b. Failure reporting , especially from controlled groups, such as

customer service.

c. Critical Incident Studies (called RSO's in IVDRT because they are

not "critical" in a nuclear industry!). This is a powerful and

perceptive tool for product design.

d. Accident/ incident reporting systems .

Data reduction for management or design use is required.

38. Accident Investigation . See the new Manual. A few thorough, in depth

investigations, including a manufacturer's investigations of the role

of his systems, will provide more useful data than superficial

investigations of many hundreds or thousands of accidents. ERDA

investigations of serious events reveal on the order of forty

organizational improvement possibilities per case, about half being

system improvements.

Audits of design, production, quality assurance and other relevant

programs by high level, independent groups (internal or external) have

been shown to be powerful and searching methods of discovering needed

improvements, particularly when good audit and process criteria are used.

39. The Organization's Information System . This section extends earlier

comments and findings. Primary is the finding that EDP coded systems

in industry have produced information of modest diagnostic value, but

almost no information for action decisions.

40. National Information System . Nfe.ny pieces and parts are available but

not tied together. Therefore, a designer is placed under an unwarranted

handicap. Governmental initiative seems necessary to make diverse

information stores easily accessible to smaller organizations.

41. Measurement Techniques .

a. The Frequency-Severity Matrix is further developed (p. 420).

b. Extreme Value Predictions (p. 426) are proving to be a useful

means of estimating the probability of more serious events from

past "worst event" data.*

*Gumbel, Emil J. "Statistical Theory of Extreme Values and Some Practical

Applications," National Bureau of Standards, Applied Mathematics Series, 1954.

20
c. Simplistic rates commonly used in industry to measure industrial

safety performance are of slight value (p. 432) . Also

see Appendix K for results of an NSC Symposium on Measurement,

pertinent for many safety- related problems.

* * *

In summary, the experiences of the last six years suggest the

following needs

:

1. A compilation or synthesis of the best available practices

to form an ideal measurement yardstick.

2. Systematic investigation of accidents in sufficient depth

to modify and inprove the ideal system. (A "state of the

art" for the next three.)

3. Pilot tests and evaluations of the system.

4. Research and evaluation under conditions where variables

are at least known, even if not quantified.

5. Implementation is a long-term project, five to ten years.

However, short-term gains result from each improvement;

differences can be seen within a year.

These needs apply directly to product safety and commercial

transportation, and perhaps other fields as well.

21
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23

mrOTHESIS GENERATION FOR RARE EVENTS RESEARCH

Ludwig A. Benner, Jr.

National Transportation Safety Board

LUDWIG BENNER, JR. is Chief of the Hazardous

J^terials Safety Division of the Bureau of Surface

Transportation Safety, National Transportation

Safety Board. Mr. Benner has long been involved

with transportation safety in a number of capacities.

His paper deals with the process of discovery,

suggesting that hypothesis development in accident

investigations and rare event research need not be

a hit or miss proposition based primarily on

"creative intuition" and "good luck." Rather,

Benner proposes a multilinear events sequencing

methodology to aid in the development and testing

of research hypothesis. The interested reader is

referred especially to Benner, L. , Accident

investigations: Niiltilinear events sequencing

methods. Journal of Safety Research , 1975, 7^(2),

67-73, for a more complete discussion of the

proposed methods.

INTRODUCTION

This paper focuses on hypothesis generation. How does one generate

propositions that can be tested by scientific methods? Popper (1959)

says there is no logical path leading to new ideas --they can only be reached

by "emfuhlung" or creative intuition. Polya (1957) offers a "rule

of discovery" that goes about like this: the first rule of discovery is to

have brains and good luck; the second is to sit tight and wait until you

get a bright idea. Their views are widely held.

Surry's (1969) discussion of accident research methodology is useful if

further understanding of some of the difficulties with existing accident

research are of interest to the reader. But Surry does not discuss the

discovery problem.

The problem of structuring discovery, especially the discovery of

hypothesis, has been with us for a long time. There may be a way to do it.

I would like to share with you my method for generating hypotheses, derived

from my work as an accident investigator.

WHAT HAPPENED?

After an accident, every investigator is confronted with the need to

answer the question "what happened" regardless of the ultimate purpose of

his investigation. The usual approach is to try to "reconstruct" the

accident. The method used is to try to isolate events suggested or indicated

by evidence acquired after , the accident. As the investigator becomes aware

of events that occurred during the accident, outlines of what happened

25
begin to emerge. As additional evidence of events comes to light, the

investigator begins to speculate about possible hypotheses, that is,

ways the accident might liave happened. Each hypothesis is tested against

the evidence subsequently developed, to arrive at the most likely

explanation of what happened.

As I have observed this process, elements common to the search for

understanding of any phenomenon have been noted. These observations

suggest that there may be a logical path leading to new ideas, and that a

general method for generating hypothesis during the study of phenomena,

including rare event phenomena, may be possible. The essential assumptions

and principles follow.

EVENTS SEQUENCING

My hypothesis generation method is based on the premise that the

functioning of our universe and its constituent parts reflects a continuum

of interacting events. Events, in this context, are used in the sense that

someone or something does something (actor + action = event) . Each event

influences one or more events which follow that event in time. It is the preced

follow logic of the related events that provides the key to the hypothesis

generation method.

The accident investigation process is based on a "break down events"

principle. Take "an accident" and break it down into increasingly finite

events in the following manner. "An accident occurred" describes a

phenomenon as a gross event. "A sliding car struck a tree" breaks down the

gross event into two subevents . The car rolled onto an icy patch, began to

slide, and struck a tree further breaks down the phenomenon into even more

discrete events. This "break down" process can be continued for as long as

necessary to gain the understanding of the phenomenon required by the purpose

of the study. Each time an event is subdivided, the need for more precise

understanding of the actor- action relationships arises. And each time

the need arises, the last known action by an actor provides a starting point

to hypothesize the next action or actions that must have been taken by that

actor in order for him to arrive at the next known action supported by the

evidence. Thus, the bridging- of the events gaps is circumscribed by logical

spatial and temporal relationships among the events as they progress through

their precede/follow sequence. This method of "breaking down" the events

sequence structures the discovery of unknown events required for the

sequence to proceed from the beginning point to the end point of the

phenomenon being studied.

Usually for someone or something to do something (an event to occur)

certain enabling conditions must exist. The creation of these conditions

also flows from an event sequence. That is to say, events produce changes

of state or outcomes. For any phenomenon under study, the chronological

flow of events provides an explanation of what happened, just as we

naturally try to create mental movies when we attempt to describe events.

The existence of the enabling conditions , which must have been present for

each event to occur, can be traced backward in time to explain "why" the

events sequences occurred.

26
A convention for displaying the events sequences, which further

facilitates discussion and discovery, has been proposed where the events

sequences involve two or more actors (Benner, 1975). This multilinear events

sequencing method provides opportunity for a precede/follow logic check along

both the horizontal time coordinate for a single actor as well as a vertical

time coordinate for sequencing related events by two or more actors. In

other words , the timing of any event by any actor can be compared with any

other event by any other actor, and this chronological validation provides

a method for "proving" the hypothesis that differs from traditional,

statistical, or experimental approaches of the scientific method. The

display has the further advantage of highlighting unknown "linking" events

in the sequence. It can also structure speculations about their occurrence

or guide the search for evidence to confirm these speculations

.

RARE EVENTS RESEARCH

The multilinear events sequencing methodology can be useful for

predictive study of rare events or accident phenomena. If one can

accept that accidents are multi-event phenomena involving more than one

actor, whose actions must occur in a specified chronological sequence to achieve

a harmful or other outcome of interest, it can readily be seen that if

any of the events occur out of sequence (or not at all) the outcome being

studied will not occur. Thus the pattern of events describing the "rare

event phenomenon" can be studied. It is the occurrence of the events sets

in the necessary relationship which is rare, rather than the occurrence of

individual events within the set.

If this concept is valid, it suggests new approaches for the

accumulation of data about rare events in the form of events sets , rather than in the form of individual conditions on events constituting

the phenomenon. The manipulation of chronologically sequenced events sets

in process flow chart form appears to hold more promise in understanding

rare events phenomena than the present approaches. In the accident field,

the need for a unifying theoretical framework to organize the events sets

for research purposes can be shown to be increasingly urgent. A theory which

would accommodate the sequential ordering of events sets in accident

and other rare events research has been proposed by the author (1975)

.

Summary

The sequential ordering and display of events and events sets

constituting a rare phenomenon provide a reproducible method for

structuring the discovery of a hypothesis explaining the phenomenon,

and for testing the logic of the explanation. The application of

probabilistic estimates of the frequency of occurrence of these events,

both individually and in sets, provides an approach for predicting these

phenomena. Time or spatial logic tests, as well as traditional mathematical or other experimental methods, can then be used to validate

one's hypothesis.

27
References

Benner, L. Accident Investigations: Multilinear Events Sequencing Methods , Journal o£ Safety Research, 7:2. June 1975.

Polya, G. How to Solve It , Doubleday-Anchor Books, Second Edition,

Garden City, New Jersey, 1957.

Popper, Karl The Logic of Scientific Discovery , Basic Books, Inc.,

New York, New York, 1959.

Surry, J. Industrial Accident Research , University of Toronto, 1969.

28
EPIDEMIOLOGIC APPROACHES TO INJURY RESEARCH

Julian A. Waller, M.D. , M.P.H.

University of Vermont

JULIM A. WALLER is a professor and chairman,

Department of Epidemiology and Environmental

Health in the IMiversity of Vermont College

of Medicine. Active in the field of injury

control since 1960, Dr. Waller is the author

of a large number of research papers, articles,

and books about the roles of medical conditions,

alcohol and other drugs in injury, the improvement

of emergency health services, product safety,

and other aspects of home, recreational and

highway safety.

Waller's paper begins with a brief, and

excellent, overview of epidemiology and two

basic designs used by epidemiologists for testing

hypotheses about determinants of injury, namely,

the case history and cohort methods. Waller

then discusses two epidoniologic methods based

on the interaction between the host (victim)

and the injury agent (physical energy) . The

first model presented deals with determining

causes while the second is concerned with identifying

the range of countermeasures options.

One of the unique things about the field of injury control is that

it is not a field. Rather, as best I can determine, it is a side interest

or, more correctly, a nuisance issue for several different professional

groups -- engineers , ergonomists, psychologists, systems specialists, architects, highway and vehicle builders, designers of various types, lawyers,

physicians, chemists and administrators, to mention a few. Consequently,

the construction of a unified approach to research about or control over

injury is something akin to building the biblical Tower of Babel. Each

profession has its own concepts, terminology, and acknowledged experts,

all of which are largely unknown to members of other professions who

may be equally concerned about injury as a social and economic problem.

This fact has been repeatedly brought home to me as, during the

past several months of a sabbatical, I have attempted with increasing

frustration to write a book covering all aspects of injury control.

It is almost impossible to search out all the sources where appropriate

literature or information might be found, to always understand what is

being said once I have obtained the data, or to translate my material

into language that will be sufficiently acceptable to all groups who

need to see it.

29
Just recently, in a long conversation with a systems safety specialist

whom I have known for some years, I suddenly realized that his conception

of epidemiology was quite different from the realities of the field,

as was my concept of the systems approach. Therefore, I welcome the

opportunity to explain to others the epidemiologic approaches , their

strengths and limitations. I strongly suspect that, if all approaches

of epidemiologists and other professionals are laid on the table, it

will be apparent that, despite differences in terminology, they often

seem to draw upon similar intellectual processes and have much in common.

I. What is Epidemiology

As one might infer, the term epidemiology comes from the study of

epidemics, or disease frequencies that are significantly above the expected

norm for a population at a given time. As communicable diseases began

to decline somewhat as a major cause of death and disability in the western

world, other uses were found for epidemiologic tools and concepts so

that now the techniques are applied more often to the study of chronic

diseases , environmental problems , health services , and the evaluation

of countermeasure programs, all areas relevant to injury and its amelioration.

Briefly stated, epidemiology is the study of the distribution and

determinants of disease or other phenomena in a population. Several

aspects of this need to be emphasized. First and foremost, epidemiology

is population based, getting its data not from theory or laboratory or

simulation, but directly from observation of the real world, with all

the concomitant advantages and disadvantages.

Second, the study of distribution implies that the epidemiologist

starts with the expectation that the phenomenon to be examined may not

be distributed randomly but rather follows specific nonrandom patterns,

and for explainable reasons.* This also means that proper study requires

examination not only of those times or segments of the population in

which the phenomenon exists, but also for the times or segments in which

it does not exist, i.e., the control or comparison population.

Here we already begin to get into trouble. A phenomenon may be

thought not to exist in a population or at a given time simply because

although present, it cannot be observed. Unlike clinical medicine, which

deals predominantly with correction or prevention of health problems

which are obvious, epidemiology deals with what is known as the "biologic

gradient" of disease. This term simply means that, if studied carefully

enough, virtually all disease will be found to vary not only in frequency

but also in severity, again for explainable reasons. Thus, a disease

may be present but not observable (i.e., subclinical) in some, mild,

^Because injury events are not random they should not be called "accidents,"

a term which has connotations of randomness (and consequently inability to

change) and also prescientific connotations of acts of God, punishment for

sinfulness, carelessness, etc.

30
moderate, or severe in others, and also fatal on occasion. The distribution

of this gradient varies with the phenomenon and the circumstances. Thus,

the epidemiologist is concerned both with frequency and severity.

Third, the study of determinants involves identifying why a phenomenon

is nonrandomly distributed as opposed to the previous question of how

the distribution is nonrandom. Here, again, some basic tenets should

be noted. In studying determinants one commonly examines the host (i.e.,

person or other living thing affected by the phenomenon) , the agent (or

factor necessary for the phenomenon to occur) and the environment which

may modify frequency, severity, or both. Also of importance may be the

vectors, or vehicles by which the agent is carried to the host.

Some nonepidemiologists with whom I have spoken are under the impression

that epidemiology seeks out single causes. While it can be and often

is used for this purpose, it is most important that one of the basic

tenets is that a single cause may have multiple effects and that a single

effect may be the result of several causal factors. In some cases, these

causal factors may be capable of producing a single effect. In other

cases, the effect may occur only if two or more factors are present simultaneously or in tandem. In the study of injury there have been far too

few sophisticated studies philosophically oriented toward and capable

of examining a multitude of factors simultaneously. This is a fault of

the users, rather than of the capabilities of the field.

Although there have been many variations, two basic designs exist

for testing hypotheses about determinants, and a brief discussion of

the advantages and disadvantages of each of these designs is warranted.

Both designs require examination of two populations over two time frames,

the so-called 2x2 model.

The case history or case-control method involves comparison of a

population that has the disease (in this case injury or events capable

of producing it) with a population that does not have the disease. It

thus starts with the second time frame, that is after the disease has

occurred. Then, through questioning, study of old records, etc. this

method attempts to determine how often factors hypothesized to be causal

existed during the period antecedent to the disease.

Applied to injury, the researcher would compare persons fatally

injured in crashes with those not involved in crashes to determine how

often each group had alcohol present. The "hooker" is that since the

data are from the real world the populations being compared may differ

also in many factors other than alcohol, some of which may be equally

or even more relevant to the occurrence of injury events. Thus, the

epidemiologist attempts to match the ill and well populations for as

many variables as possible, leaving unmatched only those which are subject

to hypotheses.

The advantages of the case history method are that it is relatively

quick, inexpensive, and can be applied to rare events. The disadvantage

is that it cannot be used to describe the absolute frequency with which

31
the disease occurs in populations with or without the causal factor in

question. For this, one must turn to the cohort method which, in turn,

has disadvantages of high cost, much longer time frame for completion

of the study, and inability to examine rare events.

The cohort method is the exact reverse of the case history approach.

The two populations identified are those with and without the variable

or variables hypothesized to cause disease or to affect its severity.

Both populations are then followed over a specified time, and the resulting

proportions with disease or with greater severity are then compared.

Again applied to injury, using the case history method one could

say that 42% of fatally injured drivers but only 3% of drivers not in

crashes but with similar driving exposure have blood alcohol concentrations

of .10% by weight or greater. Using the cohort method, it would be possible

to say that the risk of crashing per 100,000 miles of driving is pi with

no alcohol present and P2 with a BAG of .10%. Of course, the cost of

following two such populations using the cohort method is prohibitive,

and there are very serious and insurmountable ethical issues regarding

permitting persons impaired by alcohol to drive and to expose themselves

and others to the risk of crashing.

II. Relation Between Epidemiologic and Other Methods

What are the relationships of epidemiologic methods to other ways

of studying injury events for purposes of establishing countermeasures?

Important similarities and differences exist. One similarity is the

creative process. Whether the method involves epidemiology, psychology,

system design, simulation, or any other approach, the result will be

no better than the capability of the researcher to do modeling, that

is, to identify all of the potentially relevant cells or branches, to

establish cogent hypotheses , and to design acceptable methods for testing

them. I would suggest that the approach to an injury problem commonly

goes something like the following:

1 . Hypotheses are established based on anecdote or unorganized

observation.

2. The hypotheses are tested through epidemiologic, sociologic,,

or possibly engineering analysis of real world experience and through

selected laboratory simulation.

3. Building upon data about frequency, severity, and causal factors

so obtained system designing then begins to take place, identifying all

possible component branches that need to be considered, dealing with

types of failures that may occur, relative probabilities and likely results.

Of course, one can design a theoretical fault tree involving a totally

new product or situation. But even here the designer builds upon previous

experience using data drawn from other potentially applicable situations.

4. Testing and further development of the system model takes place

through additional epidemiologic, laboratory and other studies, including

simulation.

32
5. Priorities for coimtermeasures are established based upon selection

of those aspects of the problem that seem to be associated either with

greatest frequency, severity, or both, and that simultaneously have greatest

likelihood of feasibility. By feasibility, I refer not only to technical

and economic issues but also to social, legal, cultural, and other issues

that form the warp and weft of human society. For, as Henry Wakeland

has aptly noted, this nation "has never been satisfied to serve only

one set of values". ^ Wakeland has recently published a paper i^^ich considers

18 values related to safety and other social issues in assessing the

expected success of different countermeasures . -I- These values can be

further grouped into the following categories:

a) economics

b) public image and psychological motivation

c) equality and fairness

d) deservedness of protection

e) critical position in a technical system

f) timing

6. Finally, one or more countermeasures may be applied. If fortune

smiles, arrangements have been made to permit adequate evaluation. Here

again, epidemiologic methods may come into play.

It must, of course, be immediately apparent that the methods and

concepts used by epidemiologists are not limited to this professional

group, any more than methods of other professionals are used by them

alone. Several of the above steps, and occasionally even all of them,

may be carried out either by a single individual or professional group,

or by members of a number of professions

.

I hasten to note that most of the epidemiologic research in the

field of injury control has been concerned with examining the distribution

and determinants of injury events and of the severity of such events.

This has led to proposals for countermeasures , the effectiveness of which

has been evaluated in relatively few cases.

Almost entirely nonexistent has been either epidemiologic or sociologic

research into the "process" by which injury control priorities are either

established and implemented, or sought but blocked. Why, for exan^Dle,

despite years of documentation about their value is it so difficult to

obtain adequate regulations and legislation for use of seatbelts and

other passenger restraints or to keep such legislation for motorcycle

helmets? Why at the same time is there such concern, effectively translated

into congressional action, about the safety of school busses, when a

bus program may save the lives of only 30-40 persons per year, and then

only at great cost?

Why has the National Transportation Safety Board had such a poor

batting record in convincing others to adopt its countermeasure proposals

despite extensive and thoughtful system modeling? Recent studies from

the National Bureau of Standards show that sodium chloride mordant in

i:5)holstery fabrics may add to the toxicity of fumes when such fabrics

33
bum. Why is there resistance within the Department of Commerce to applying

the results of this work toward reduction of deaths from fire? Research

is no more useful than the applications to which it is put. And much

more research about the whys and why nots of this application process

is needed.

I noted earlier that in looking for causal factors that might affect

frequency and severity the epidemiologist seeks out clues about the host,

agent, and environment. Through work by Gibson^ and by Haddon^ the agent

in injury events has been identified as physical energy (chemical, thermal,

kinetic, electrical, or radiation) transferred to the body in sufficient

quantity and at rapid enough rate to damage tissues . The following are

two epidemiologic models based on the interaction with this agent. The

first model is concerned more with identifying causes wMle the second

deals with identifying the range of countermeasure options.

III. A Model for Injury Occurrence and Outcome

The safe use of energy that has been massed by man, or the safe

exposure of humans to forms of energy massed by nature, depends on two

generic factors --the level of functioning of the person and the demands

of the task inherent in making the energy serve the functions we wish.

Each person has certain capabilities which vary from moment to moment

and from one person to another. One of these capabilities is one's knowledge

about one's self in relation to different aspects of the environment.

Such knowledge depends upon basic intelligence, experience, education,

short and long term memory, and attitudes and belief systems which one

may bring as cultural heritage. Another capability is the ability to

receive information about the environment through inherent senses such

as sight, hearing, touch, smell, taste, vibratory sense, and vestibular

function.

Yet a third attribute is the ability to make rapid judgements about

one's self in relation to the environment as a result of the combination

of information received through the senses and knowledge applied in interpreting

such information. Finally, there must be the capability to act in response

to judgements that suggest danger may exist. In order to act effectively

to the variety of tasks that we must perform daily, a person usually

must have range of motion, strength, stamina, speed, and balance.

In summary, therefore, each person must have the capability to receive

information correctly, process it in timely fashion, and react appropriately.

What are some common task demands? Some tasks are extremely con^lex,

requiring extensive learning, judgement, intelligence, or all three.

Other tasks require use of several senses simultaneously, or the ability

to pay attention to multiple stimuli or signals at one time. In other

cases, there is a requirement for quick action, dexterity, strength,

balance, or stamina. Tasks may vary in demand not only from one task

to another, but also for a single type of task over time. In general,

the more automated the task the easier it is to perform and the more

consistent is it likely to be.

34
The Pre-Injury Phase

Let us now put the person with his or her capabilities and limitations

together with the task and its unique set o£ demands. As long as the

actual performance of the person exceeds the demands of the task at all

times there is no likelihood that an event potentially capable of producing

injury will result from the interaction. If for any reason, however,

the task exceeds the performance level the energy being managed or controlled

by the task is no longer in control and may be available to cause injury.

This moment at which task demand exceeds the performance is commonly

referred to as an "accident" by the public.

Three types of situations exist in which the demands of a task may

momentarily at least exceed the performance of the individual. First,

a person may suddenly or chronically function at a level of performance

below the average for most people. This can happen because of an acute

or chronic medical condition such as epilepsy, diabetes, heart disease,

mental illness, or senility, or because a person is temporarily under

the effects of a drug like alcohol or carbon monoxide or is extremely

young.

There is also some documentation that lower performance may occur

during the premenstrual and menstrual parts of the normal menstrual cycle,

and conceivably during some hours of circadian cycles . Inexperience

with the particular task, or certain social or societal conditions and

pressures may also lead a person to function at less than usual performance

level, an exan^le being the driving behavior of a teenager in the presence

of peers.

Another way in which demand may exceed performance is because the

task either is continuously difficult or has suddenly and temporarily

become substantially more demanding. This may happen for various reasons,

some common and some unique. As the task increases in demand the performance

level of the person also increases somewhat, but often not enough to

prevent demands from exceeding performance at least on occasion. The

change on the part of the person represents utilization of some of his

or her spare capacity until maximum performance level is reached in order

to attempt to avoid what has been perceived by the person to be an impending

disaster as the task gets increasingly out of control. Spare capacity

refers to the level of performance a person is potentially able to produce

at any given moment in order to prevent task demand from exceeding perfoimance

level

.

We are now ready to examine the third type of failure situation,

one that is commonly overlooked because people tend to think only of

human failure or task overload. In this case both the person and the

task contribute to the event. The person may be temporarily or consistently

functioning at somewhat less than average level at the same time that

the task is tenporarily or consistently somewhat more than usually demanding.

Thus, because of joint contribution the two lines are close together

and have significantly greater than average likelihood of crossing.

35
Why is this sort of relationship so often overlooked when it may

in fact be the most frequent mechanism in the initiation of injury events?

There are probably two reasonable explanations. First, most of us are

taught from grade school on to oversimplify explanations of causation.

Thus , we are more likely to be trained for and attuned to seeking single

causal factors than to identify and tease out more complex etiologies,

perhaps involving several conditions acting simultaneously.

Probably equally important, many of the relative increases in task

demand are so common and so subtle that most of us respond to them subconsciously, and we do not realize that it is only because we usually have

sufficient capability to maintain a fair degree of spare capacity that

we are able to effectively deal with sudden and sometimes unnecessary

increases in task load without disaster.

Given the information about the interactions of humans and tasks

in the pre-injury phase, it should be possible to combine the examples

of varying human capabilities and different task demands, and spare capacity

into a single diagram. This has been done in the figure which shows

that as the task gets more demanding, it (a) reaches a point at which

it is beyond the capability of the least competent (with respect to that

task) members of society, and (b) reduces the amount of spare capacity

that more competent members may have remaining at any given moment so

that they can avert disaster if there is a sudden further increase in

task demand, a sudden decrease in their own performance, or both.

Let us assume, as shown in this figure, that a point has been reached

at which task demand exceeds performance level and the real or potential

energy that is being managed is now no longer under control. At that

moment the pre-injury phase has been ended and the injury phase of the

event begins

.

The Injury Phase

The fact that energy is out of control does not in and of itself

mean that an injury must necessarily occur. Several intervening conditions

determine whether injury will occur and how severe it will be. The basic

principles are the following:

1. The greater the mass of energy that exists and is released,

and the more rapid the release, the greater the likelihood that injury

will occur and that it will be severe.

2. If the energy reaches tissue, the rate of the transfer (ideally

described in units of energy per unit of body tissue per unit of time)

determines the severity of injury.

3. Severity is also determined by inherent characteristics of the

tissue itself and of the organism.

36
puDoidp >|SD4 JO douDiujopsd p |aAa~i

37
An Alternative Pathway

Although all unintentional injury involves damage by misapplication

o£ physical energy some such events occur through a mechanism other than

the unintentional transfer of energy from an external source to the person.

The body carries out its own internal mechanisms for energy management

that permits us to maintain a balance or homeostasis with the environment.

An event that interferes with this homeostasis can also cause harm through

energy misapplication. Examples include drowning, some types of poisoning,

and exposure to extreme cold.

Post Injury Phase

One further generic factor determines the ultimate outcome of injury.

This is the entire series of actions that occur after the injury and

which may result at one extreme in early rehabilitation without permanent

harm, or at the other extreme in either death or continuing disability.

Data suggest for example that somewhere between 15-25% of persons viho

die from highway crashes might still be alive if emergency care were

more readily available and of better quality.

Innocent - and not so innocent - Bystanders

One of the questions that is sometimes raised by people ^fAlo consider

the energy management model just described is whether it takes into account

the apparently common occurrence in which an innocent bystander is injured.

The answer is yes . We need to consider two types of situations , that

in which the individual who is injured clearly is an inadvertent victim,

and that in which he or she only appears to be so.

The model presented indicates that if an energy management task

is greater than the individual's capability of dealing with it the energy

may go out of control. From that point on the errant energy may be available

to injure the person who was originally handling it, or it may create

damage to any other people or structures that happen to be in the immediate

vicinity. Thus, the driver of a bus or pilot of a plane who loses control

of the vehicle may take with him not only his passengers but, especially

in urban areas, many others who are only circumstantially associated.

Can this be described as a random event? It can only in a very

narrow sense. One may not be able to predict which particular innocent

bystander is likely to be injured. But it may be possible to prognosticate

fairly accurately how many such persons, of what types, and under what

conditions. Socioeconomic, cultural, and legal circumstances, for example,

determine the degree of crowding that may exist in an apartment house

,

or on a bus, and the likelihood that the particular bus or building meets

specific safety codes. Federal, state, or local standards may dictate

whether a plane, or a truck with high energy explosives, is permitted

to travel through areas that are heavily populated or whether precautions

have been taken so that even if the energy is out of control it will

damage relatively few unsuspecting persons.

38
Let us now look at the not so innocent bystanders. Surprisingly,

there are more of these than is commonly thought. One group of not so

innocent bystanders is easily identified- -people who stand around and

observe arguments, fights, fires, and other disasters and who consciously

run the risk of being drawn into a potential chain of damaging events.

Another group is individuals who are seriously or fatally injured

as passengers of drivers impaired by alcohol. There is now strong evidence

that such persons as a rule also have been drinking and usually are as

impaired as is the driver of the vehicle.^

What about people who are lost in ravages of floods, tornadoes,

earthquakes , or volcanoes? Surely they must be innocent victims . Information

suggests that in fact this may not be the case. One is the long history,

going back into antiquity, of rebuilding homes and even entire cities

at the same location where previous ones were just destroyed by "natural

events" with high probability of reoccurring. Furthermore, such redevelopment

may use precisely the same methods of construction that were shorn to

be noneffective in the past. Finally, in contrast to this ignoring of

long-term warnings, there is the deaf ear turned to notices of immediate

danger.

Thus, in the presence of natural massings of potentially destructive

energy, people through all of the methods described above do not function

in a manner most conducive to keeping the energy within some modicum

of control, i.e, in a way that will limit its harmful effects on them.

Such individuals cannot be called innocent bystanders. (It must be emphasized

that this statement is not as pejorative as it appears on first reading.

Although persons who ignore warnings about imminent disasters may be

acting foolishly, those who build or rebuild in known hazardous locations

or ways may be doing so because they personally have no other options

because of shortages of land, money, etc. The "blame" for such persons

being at greater risk may rest with the community or society rather than

with the individuals.

IV. A ]ybdel for Countermeasures Against Injury

Before describing the range of options for reduction of injury and

its outcomes , we need to examine first some important questions concerning

relationships between what is known about the mechanisms of injury events,

and what actions may be appropriate to reduce the frequency and severity

of injury. Appropriate countermeasures to a specific type of problem-

whether it be injury or illness--can be derived logically from what is

known about the natural history of the event and its circumstances.

But, contrary to common opinion, they do not necessarily flow obviously

from such knowledge.

The difference between obvious and logical is that an obvious solution

is one suggested primarily by examining relative frequencies of different

factors in injury events and by attacking first the factors with highest

39
frequency. A logical solution on the other hand is one that may include

information about frequency as one of its considerations but that is

suggested primarily by examining the relative feasibility of countermeasures

for affecting ultimate outcome of death, disability, and discomfort and

for having limited unwanted side effects such as excessive economic or

social costs. Occasionally, an obvious solution is also a logical solution.

The ideal logical solution to a health problem is one that can be

applied universally and that works with a very high degree of effectiveness

once applied. Such ideal solutions often do not exist, however, and

one may have to be content with logical solutions that are applicable

to helping all people only under more limited circumstances or to fewer

people over a wider range of events. The appropriate approach in this

case to dealing with a particular type of injury or other health problem

would be to put together a network of somewhat overlapping logical solutions

that have high effectiveness for limited situations or limited but acceptable

degrees of effectiveness for wider situations so that in combination

these partial solutions can bring about substantial reduction in injury

frequency and severity.

The model for injury control^ developed by Dr. William Haddon starts

with the concept of physical energy as the agent in injury events and

asks in progressive order with relation to the previous model what methods

exist for limiting the harmful effects of that energy on people and property.

Here is his list of logical solutions.

1. Prevent the initial marshalling of the form of energy.

2. Reduce the amount of energy marshalled.

3. Prevent the release of energy.

4. Modify the rate or spacial distribution of release of energy

from its source.

5. Separate in space or time the energy being released from the

susceptible structure.

6. Separate the energy being released from the susceptible structures

by interposition of a material barrier.

7. Modify the contact surface, subsurface, or basic structure which

can be impacted.

8. Strengthen the living or nonliving structure which might be

damaged by the energy transfer.

9. Move rapidly in detection and evaluation of damage and counter

its continuation and extension.

10. Carry out all those measures which fall between the emergency

period following damaging energy exchange and the final stabilization

of the process (including intermediate and long-term reparative and

rehabilitative measures)

.

40
This series of options is both unique and interesting because it

places the anphasis on dealing with the energy at all stages that lead

to and can affect ultimate outcome instead of eraphasing primarily how

humans can be modified, and particularly doing so in the pre- injury phase,

as has been the most common approach for many years. Changing people

is not excluded per se in this series ; it is one of the possible methods

available to prevent the release of energy. Reducing task demand is

another method appropriate here.

only problem- -and it is a minor one- -with the Haddon model is

ray belief that especially within the third option alone there exist many

potential countermeasures whose details could be spelled out more explicitly.

Human performance, for example, can be maintained at satisfactory level

for specific tasks at least theoretically by the following means:

a) Limit exposure to certain tasks either voluntarily or legally

only to individuals who are capable of performing them.

b) Educate people so that they have requisite knowledge about the

nature of task demands and knowledge and skills so they are able to deal

with these demands.

c) Manipulate those attitudes and behaviors of people that may

be amenable to conscious control through a combination of education about

reasons for appropriate attitudes and behavior, peer pressure, and laws

and regulations.

Turning to task demands , these can be altered in the following manners

:

a) Simplify the task so it puts less of a burden on single senses

and permits one to assess the same information with equal effectiveness

using other sensory routes.

b) Simplify the task so it requires less intelligence, learning

or memory.

c) Simplify the task by making cues more easily visible, legible,

and less subject to visual confusion.

d) Simplify the task by not requiring simultaneous attention to

two or more cues.

e) Simplify the task by neither providing stimuli so quickly that

the individual cannot respond to all within the time available (as may

occur in rush hour traffic) nor so slowly that the individual becomes

bored and is unable to concentrate on that task.

f) Simplify the task by not putting controls of similar design

so close together that they may be confused.

41
g) Sinplify the task so it is not possible to turn on a piece of

equipment inadvertently while part of the body is near a portion of the

equipment that can create harm.

h) Reduce task demand by not leaving out important information

that the individual needs in order to assess the environment. This concept

includes a sufficient repetition of information so that it is not lost

entirely if, for whatever reason, it is overlooked the first time it

is available.

i) Reduce physical demands of the task by decreasing the amount

of strength, speed, stamina, balance, or range of motion required.

j) Finally, make the task so demanding that persons not competent

to perform it well will be unable even to start the activity and thus

by physical means will be protected from having any exposure to the hazard.

These ideas I'm sure are quite familiar to those who specialize

in human factors engineering.

V. Comments About Past and Current Research

Several important limitations exist concerning injury research as

it has been and is now being carried out. First, as already noted, research

about the process by which ideas and data are converted to action programs

is almost entirely absent.

Second, regarding another issue already alluded to, very few studies

have sought to examine a range of potential contributory factors simultaneously

in a manner that would permit observation and assessment of interactions.

Even where such examination has occurred, as in the multidisciplinary

accident investigation program of the National Highway Traffic Safety

Administration, the emphasis has been on more obvious types of failures

or problems , whether involving humans or the product/environmental complex.

Studies to explore more subtle interactions , such as shown in the figure

,

just don't exist in the multidisciplinary- endeavors . I do not know if

this absence is because few people are aware of the concept or because

the technology for teasing out the subtle is felt as yet to be too much

in its infancy.

This absence of such studies is especially surprising since several

laboratory type efforts for the Department of Transportation suggest

that there is potential pay dirt in combining human factors and epidemiology.

Such combined methods could determine to what extent and under what circum- i stances theoretical problems identified through laboratory studies actually

result in real world problems.

In illustration, studies for DOT indicate that drivers in several

late model American made automobiles have only about 40-70% of possible

maximum visibility available to thern^, and that in most automobiles manufacture

in the early 1970 's drivers in the top and bottom 20% of size have difficulty

in seeing or reaching all control devices when wearing seatbelt and shoulder

harness." Consumer Advisory Booklets just issued by NHTSA show that

42
the braking performance to get a car from 60 to 0 raph for 1976 car models

ranges from 159 to 250 feet.^ For 1976 tires placed on a fully loaded

car the reserve capacity ranges from 01 to 25^.^ So what?! It's about

time we knew what this means in real world crash experience. One report

about crashes of large trucks suggests that as many as 900,000 such events

annually may be attributable at least in part to limitations inherent

in the design of current rear view mirrors and other problems of limited

vision on these vehicles. ^0

Turning to product safety, ceramic top stoves are now made with

burners that do not change color when they get hot. Theoretically, this

subtle increase in task demand represents a problem for, among others,

the person who lias reduced vision and heat sensation because of aging,

or the person who is distracted. But what does it mean in terms of real

events? I ask that question only academically as a epidemiologist.

As an administrator concerned with injury control I have very strong

feelings that, given the information that already exists about the behavior

of children and of housewives under pressure, and the physiology of aging,

manufacturers should have had more sense and more sense of responsibility

than to market such a potential hazard in the first place.

Third, attention should be directed to cultural contributors to

injury events. I refer here to two different phenomena. One of these

is the fact that when a new product or pattern of functioning is introduced

into a culture it often appears to be associated initially with a very

high injury rate during a learning period. Some of this may be because

the product itself commonly is still in prototype state with important

hazardous bugs to be worked out. This seons to be the case, for instance,

with the snowmobile.il

But an important part of the problem also appears to be absolute

or relative ignorance by users and others exposed about rules of use

and potential hazards. A good example is the pattern of problems associated

with the introduction of the automobile to the United States 75 years

ago and to many of the so-called developing nations now. A paper about

traffic problems in Sudan^^ presented in 1975 documented that even such

simple rules as on which side of a traffic island one should drive may

be nonexistent in some places where there a^e still very few cars. Education

probably is useful during this early phase. But, because it is useful

early we tend to think it is still just as useful after the passage of

years; and this assumption may not be correct.

The other cultural phenomenon is that different populations vary

in what is expected or permissable regarding acting out, relating to

each other and relating to the surrounding environment. This means that

there may be important cultural variations in the frequency and causation

of injury events, in seeking of care once such events occur, and in the

potential success of specific countermeasures . By and large, this aspect

of injury and injury control has not been explored because few sociologists

have been interested in injury as an area for research, although recent

conference proceedings edited by Dr. Alphonse Chapanis represent an important

entree of human factors specialists into this field. 1^

43
Fourth, some very rare but exceedingly catastrophic forms of injury

events now are on the verge of becoming predictable, and research about

responses to such predictions is warranted. I refer to the fact that

it is now possible to warn people about iraminent tornadoes and tidal

waves, and that similar capability almost exists for avalanches and earthquakes

One study suggested that observable differences in death rates from tornadoes

in northern and southern United States may be largely attributable to

differences in resident responses to warnings. -'-^ Since the capability

to predict and to warn is likely to precede the capability to prevent

by several years at least, we had better have some rather good information

about what available countemeasures are likely to produce.

Finally, one of the inportant problems of dealing with real world

phenomena, usually after the fact, is that the quality of data, especially

those collected through official sources, can only be described as generally

execrable whether one refers to information about the extent or nature

of populations at risk, frequency of injury events, severity, causation,

or countermeasures . In illustration, one research group reported that

61% of the motorcycle crashes resulting in treated injuries or death

that they found were not listed in the official police statistics .^^

Another study identified 668 contributory factors among 104 randomly

selected motor vehicle crashes in lowa.^^ Fifty percent of these factors

were reported to be vehicle related, 31% involved the environment, and

19% the driver.

According to the author of the study, "the results of this investigation

appear to contradict the prevalent concept that 85% of all motor vehicle

accidents are due to driver malfunction. This concept results from a

rather consistent reporting on the part of the National Safety Council.

If the sources of information are examined, the apparent contradiction

is understandable. Individual states report their yearly traffic accident

experience to the National Safety Council on a standard fom. This form

allows for 12 contributing circumstances to motor vehicle accidents.

Two relate to the vehicle, and the other 10 relate to the driver. There

are no roadway circumstances allowed.

If the results of this investigation were to be reported within

the confines of the standard summary form, the total number of contributory

factors in the 104 accidents would have been reduced from 668 to 140,

and 125 would be driver related. Within the context of the source material

available to the National Safety Council, this sampling of accidents

would be analyzed to indicate 89% of the contributing circumstances were

driver related. The majority of the contributory factors could not be

tabulated."

Lack of awareness of this problem is especially important because

it shapes everything from the initial hypotheses to the end results of

the many researchers who only incidentally do research about injury instead

of engaging in such activity seriously over several years . Such persons

commonly do not stay long enough to learn about and avoid the pitfalls

of the data. To paraphrase Dante, "all hope of valid data abandon, ye

who enter here". But drawing also from a recent short story by Isaac

Bashevis Singer, 18 even in hell one can continue to strive for improvanent

.

44
References

1. Wakeland, H.H. An array o£ social values for use in analyzing the

need for safety regulation, Proc. 4th Intl. Congress on Auto Safety , July 14-16, 1975 . p. 875-906, NHTSA, U.S. Department of

Transportation, Washington, D.C. , 1975.

2. Gibson, J.J. Contribution of experimental psychology to the

formulation of the problem of safety - a brief for basic research.

Behavioral Approaches to Accident Research , pp. 77-89, Association for

the Aid of Crippled Children, New York, 1961.

3. Haddon, W. Jr. Exploring the options. Research Direction Toward the

Reduction of Injury , pp. 38-59, National Institute of Child Health

and Human Development, DHEW, Washington, D.C, 1973 (EHEW Publ.

#(NIH) 73-124).

4. Waller, J. A. Factors associated with alcohol and responsibility for

fatal highway crashes. Quart. J. Stud. Ale. 33:160-170, 1972.

5. Haddon, W. Jr. On the escape of tigers: an ecologic note. Am. J. Pub.

Health 60:2229-2234, 1970.

6. Bamoski, R.L. , Maurer, J.R. , and Kugler, B.A. Evaluation of direct

visibility for automotive passenger vehicles by a figure of merit.

Measurement Analysis Corp. Nferina Del Ray, California, August 1969,

(DOT Contract FH- 11 -6893).

7. Woodson, W.E. , Conover, D.W. , Miller, G.E. , and Selby, P.H. Motor

vehicle instrument and control location, accessibility, and identification, Man Factors, Inc., San Diego, Calif., July 1969,

(DOT Contract 11-6907).

8. Brakes. A Comparison of braking performance for 1976 passenger cars

and motorcycles. Consumer Aid Series Vol. 6, Part 1, January 1976,

NHTSA, U.S. Department of Transportation.

9. Tires. A comparison of tire reserve load for 1976 passenger cars

and motorcycles. Consumer Aid Series Vol. 6, Part 2, January 1976,

NHTSA, U.S. Department of Transportation.

10. Reiss, M.L., Lunenfeld, H. , and Morton, G.W. Field of view requirements

directly behind trucks and buses. AIL, Div. of Cutler-Hammer,

Deer Park, N.Y. , 1972, (DOH Contact HS-112-1-162)

.

11. Waller, J. A. and Lamborn, K.R. Snowmobiling: Characteristics of

owners, patterns of use and injuries. Acc. Anal, and Prev. 7:213-223,

1975.

12. Malik, M.A.O. and Hakim, H.A. Road traffic accidents in a developing

country. Presented at 5th Intl. Conference of Intl. Association for

Accident and Traffic Medicine, London, September 15, 1975.

45
13. Chapanis, A. (Ed.) Ethnic variables in human factors engineering , Johns Hopkins Press, Baltimore, 1974.

14. Sims, J.H. and Baumann, D.D. The tornado threat: coping styles of

the North and South, Science 176:1386-1392, 1972.

15. Riggins, R.S. , Kraus, J.F. , Franti, C.E. , and Drysdale, W.F.

Motorcycle collision injuries, Intl. Congress on Automotive Safety

(erd) Proceedings , San Francisco, July 15-17, 1974, Volume 1,

Supplement, p. 4-1 to 4-22, U.S. Department of Transportation,

Washington, D.C., 1975, (DOT-HS-801-480)

.

16. Brown, G.W. Analysis of 104 Eastern Iowa motor vehicle casualty

accidents, Proc. 3rd Triennial Congress on Medical and Related Aspects

of Nbtor Vehicle Accidents, Intl. Association for Accident and Traffic

Medicine Ma.y 29-June 4, 1969 . Published by University of Michigan,

Highway Safety Research Institute, Ann Arbor, 1971.

17. Singer, I.B., Sabbath in Gehenna. Story read before audience at

St. Michael's College, Winooski, Vermont, 1976.

46
NEEDED HUMAN RESEARCH AND NEW METHODOLOGICAL

CONSIDERATIONS BEING FORCED BY THE LAW

George A. Peters, Esq.

GEORGE A. PETERS is both a lawyer and an

engineer who has long been active in human factors.

As a lawyer, he has limited his practice to product

liability litigation, retaining an active interest

in engineering as it relates to the law. Mr. Peters

is the author of the book Product Liability and

Safety (Coiner Publications, 1971) and many articles

m law journals.

Peters ' presentation to the workshop is based

on the premise that it is the common law which

provides the major forcing function in safety

endeavors today. It is in the courts that "... the

vital safety issues and concepts are framed, final

factual decisions are rendered..." Peters contends

that it is time, past time really "... for the

professionals to get more involved in these safety

issues , so that valid information will be available

to the courts, and to those whose efforts could

prevent the injuries that give rise to law suits."

Most human behavioral research has been narrowed by experimental

hypotheses and procedure shaped by our academic training, peer review systems,

images of laboratory controls and physical science models, and conceptual

theories evolved from age old philosophical issues. The scope of such

research has been limited, not only by the nature of self-generated

hypotheses in truly independent research situations, but also by restrictions

implicit in contract research and industrial research organizations. Now,

nothing is wrong with this, except that the narrowing process may have so

narrowed our field of view that we've failed to perceive many excellent

research opportunities. This is particularly true in the field of safety

where opportunities abound for the talents of the research scientist, and the

results could serve to reduce the human carnage from an undisciplined modern

technology

.

Because personal safety is a primary societal concern and preventable

injuries still occur with staggering regularity, our system of law has

gradually changed and has created forces that might tend to correct this

socially intolerable situation. The cost of the human life or limb has been

rapidly escalated, under the law, so that there is greater incentive to

perform, subsidize, or apply human research. The courts are becoming

increasingly specific in delineating safety responsibilities and safety

requirements for those having some control for unsafe conditions or unsafe

acts . Thus , the increasingly important areas of safety research are those

being formulated by the courts, rather than the more traditional kinds of

hypotheses that might be generated by independent research scientists or

those performing under contract obligations.

47
The laws that should be of vital concern are not those legislative

statutes that create governmental agencies empowered to issue rules and

regulations relating to safety. This may be a highly visible enterprise

but it has little to do with the vast bulk of safety law or the concerns

of the professional safety specialist. It is the common law, or judge

created law, that is being applied each day to tens of thousands of

individual lawsuits in the local county, parish, or district courtroom

that is the major shape force today. This is where the vital safety

issues and concepts are framed, final factual decisions are rendered, and

millions of dollars are awarded on the basis of safety related conclusions.

It is where the answers are sought to a wide variety of safety issues that

could have been the subject of legitimate human safety research, or human

behavioral research, but where such answers are frequently given only by

those who can speculate or extrapolate from information that has not been

founded on any experimentally verified data. It is time for the professionals

to get more involved in these safety issues, so that valid information will

be available to the courts , and to those whose efforts coiiLd prevent the

injuries that give rise to lawsuits.

Rare Events

As to liability for rare events, let us consider the design of a toilet

paper dispenser. What type of human behavior with a toilet roll might cause

injury for which the household or premises owner might be legally at fault

and financially liable? What would be the range of foreseeable or predictable

human error? One example, part of our common law for nearly tm decades,

involved a case where a woman who became locked in a lavatory, saw an

opening above the door through which she might escape, put her left foot on

the lavatory seat, grasped with her left hand a fixture on the wall, grabbed

the top of the door with her right hand, then placed her right foot on

the toilet roll and its dispenser. She then decided that it would be too

acrobatic to climb over the door, so she started to return to her original

position, but somehow shifted her weight on the toilet roll and it

rotated causing her to lose her balance and fall to the floor where she

sustained moderate injuries. The Judge stated that "She must be taken

as having acted entirely rationally," and damages against the householder

were allowed. (Sayers V. Harlow Union District Council, 2 All E. E. 342,

England, 1958).

Similarly, when a landlord failed to repair the water pipes to an

unflushing toilet, after a fire, damages were awarded to a woman who injured

her back pailing water from the bathtub to the toilet (Mitchell V. Friedman,

11 N. J. S. 344, 78 A2d 417, 1951). Thus, pailing water to an unflushing

toilet or standing on a toilet paper roll are, legally, not such rare

events or remote causes as to deny liability. Therefore, they are the

classes of human behavior that are predictable, about which data should

be gathered by someone, because liability or fault is attached to the

omission of such considerations. Now, who would perform such research?

I don't think that the manufacturer of toilet paper rolls would think it

48
1

within his province and the manufacturer of dispensers or fixtures might

be too small or believe that this is a systems , a general contractor , or

an architect's problem. So, we have an example of rare event research

and application information that's just not rolling along.

The design and layout of bathroom products is, indeed, medieval and

primitive, rather than functional and adapted to the range of anthropometric

and behavioral variations clearly foreseeable. That the bathroom is a

major source of home injuries is rather obvious. But, I know of few

human factors scientists who are vocationally preoccupied with this

particular area of research. I have seen bathrooms expanded in scope with

more space, objects, compartments, utensils, and ornamentation as builders

react to perceived buyers' tastes ... .but this merely means that there is

an expanding variety of new accident conditions being built into home

perhaps, because there is a comparative absence of research findings

relative to this essential area of our life space. This situation may

not be remedied until we have a Piaget of the bathroom who has a

Jacques Cousteau flair for dissemination of empirical findings

.

Failure to Provide Safety Devices Where Human Error Foreseeable

A young boy put his arm inside a launderette washing machine after it

had stopped its spin cycle, it then started spinning and injured the boy's

arm. An expert testified that if a door interlock had been installed, the

machine could not have started spinning with the door open, and the injury

would not have occurred. In this case, the appeals court stated that

there was evidence sufficient for a jury to find a design defect under

strict liability against the launderette owner in much the same way it

could against the manufacturer, retailer, or leaser (Garcia v. Halsett,

3 Cal. App. 3d 319, 82 Cal, Rptr. 420, 1970). This case extended the

manufacturer's liability for negligence in failing to adopt and provide

reasonable safety devices (Varas v. Barco Mfg. Co., 205 Cal. App. 2d 245,

22 Cal. Rptr. 737, 1962) to strict liability for failure to provide

safety devices such as interlocks. Obviously, such interlocks must not

themselves be unreasonably susceptable to a fail unsafe mode, a

malfunction associated with a foreseeable misuse, or an intentional

suppression of function.

Failure to Compensate for Human Clumsiness

A coffeepot shattered and flying glass struck and injured the consumer.

It was alleged that the user had accidentally bunded it against a faucet

while filling it with water, that this may have cracked it and ultimately

caused it to shatter upon heating. The court decided it was a jury question

whether the coffeepot was defective, given an insubstantial bumping during

an intended and foreseeable use.

49

1
Failure to Provide Auditory Warning

A construction worker was killed when a front end loader backed over

him because the driver could not see the worker, who stood about 30 feet

away, due to a blind spot. An expert testified that the blind zone could

have been reduced by mirrors and the danger also reduced by an audible

backup warning (Pike v. Frank C. Hough Coiipany, 2 Cal. 3d 465,

85 Cal. Rptr. 629, 467 p. 2d 229, 1970).

Failure to Provide Adequate Vision

A young child, standing in front of a bakery truck, could not be seen

by the truck driver who started forward and injured the child.

The bakery truck attracted children who purchased the bakery products

being sold from the truck and, therefore, the truck was equipped with a

mirror so that the driver could see in front of the bumper. However, there

was still a blind spot, and an expert testified that additional mirrors

would have prevented the accident (Menchaea v. Helms Bakeries, Inc.,

68 Cal. 2d 535, 67 Cal. Rptr. 775, 439 p. 2d 903, 1968).

Label Warnings

In 1965 (in Hubbard -Hall Chemical Co. v. Silverman 340 F. 2nd 402,

1st Cir.) , a Federal court held that a printed warning of danger was

insufficient on an insecticide label, that skull and bones or similar

pictoral symbols were also necessary and, for the failure to include the

pictoral symbol, the manufacturer could be held liable for any injuries,

such as insecticide poisoning, proximately caused by the omission. Why,

because it was foreseeable or predictable that farm laborers may have

limited education and reading ability. Those injured were MexicanAmericans who could not read the insecticide label because it was printed

in English. Incidently, this liability attached despite the fact that

under the Federal Insecticide Act and despite the fact that the

United States Department of Agriculture had approved the label.

This underlines the well known fact that compliance with government

standards or approval by government agencies is no more assurance of

safety than compliance with voluntary concensus trade standards or

approval by industry supported organizations that certify or endorse a

product's safety. Safety standards and safety certification must achieve

quantum jun^DS in validity. However, they may continue to be accepted as bare

minimums for safety and some evidence of due care, but only in negligence

actions. In some jurisdictions, there is still some life to one of their

original purposes in aiding attorneys in the defense of lawsuits. While

still a viable insurance loss control measure, safety standards today are

relatively poor and very costly end-products of safety research. Open

publication of original research findings , as required by most accepted

codes of ethics for scientists, remains the most effective means of

disseminating scientific information. Open publication best serves the

50
ultimate public beneficiary, who (in the final analysis) actually underwrites

the cost of research. Contrast this with the restricted transmission of

scientific research to a standards formulation process that is intrinsically

biased by its concensus compromise procedures and the self-interest of those

who are typically active in such activities . This poses a moral and ethical

obligation that far too many scientists have overlooked to the detriment

of the vitality of safety research and the public interest. Research performed

in support of a standards development program, if separately published,

might prove of greater ultimate value than the standard itself.

Obviousness

In Luque v. McLean (8 C. 3d 136, 104 Ca. Rptr. 443, 501 P. 2d 1163,

1972) , a young man was injured when he slipped on wet grass and his hand

entered the discharge chute of a rotary power motor. The jury was instructed

that there could be no liability for the injuries, if the young man had

been aware of the defect at the time of the accident; that is, a distinction was drawn between obvious as contrasted with hidden defects. The

California Supreme Court repudiated this distinction, so the safety engineer must pay as much attention to obvious hazards as he does to hidden

hazards. Safety research should not depreciate obvious hazards.

How safe is safe?

Back in 1963 (in Roberts v. United States, 316 F. 2d 489, 3d Cir.)

,

where a manufacturer failed to place any warning labels on containers of

ethylene glycol, a Federal court held "one who supplies a product...

for another to use is subject to liability for bodily harm. . .if .. .from

the facts known to him should realize the product... is likely to be

dangerous for use... and fails to exercise reasonable care to inform... of

facts and conditions which make the product likely to be dangerous." This

is known as "negligent failure to warn" and employs the risk criterion

of "dangerous ."

Now, even in strict liability, the same criterion had been used,

as employed in the Restatement of Torts, second, section 402 A, in the

following context: "One who sells any product in a defective condition

unreasonably dangerous to the user or consumer or to this property is

subject to liability for physical harm thereby caused." Now, this means

that a product could be reasonably dangerous and no legal fault would

attach. Thus, product safety engineer were using this criterion as to

whether a particular risk was acceptable, tolerable, or safe. In other

words, to be unsafe, it had to be unreasonably dangerous.

51
To put this into proper context, a safety engineer searches to identifyall hazards. Then he determines the risk associated with each hazard. The

risk analysis is but a prelude to a determination as to whether the risk

is acceptable or unacceptable; this decision-making involves a personal

value judgement as to whether the magnitude of the risk is a tolerable risk

or of such a magnitude as to require some risk reduction action. It is

that value judgement that is the essence of the professional practice

of safety engineering, since each decision accepts or rejects a predictable

amount of human injury and property damage.

Certainly, this kind of decision-making requires some understanding

of what the law regards as a safe or unsafe product , process , act

,

condition, or system. Guidance is not found in the cookbook application

of design requirements, the code compliance mentality of technicians,

nor from jailhouse lawyers attempting to apply the letter of the law while

failing to understand its spirit, intent, trend, or worse case implications.

Ultimately, it could be a jury that second-guesses the safety engineer's

original decision as to whether a hazard constitutes such a risk that is

unsafe. The jury does this as a first step, before deciding the damages

to be awarded to the injured, based upon the words contained in the Judge's

Instructions to the Jury. As I have previously mentioned, the words used

the phrase "unreasonably dangerous," that is, that risks created should not

be unreasonably dangerous

.

This level of acceptable risk was reduced when the California

Supreme Court, in 1972, in Cronin v. J. B. E. Olson Corp., 8 Cal. 2d 121,

104 Cal. Rptr. 433, 501 P. 2d 1153 eliminated the term "unreasonably

dangerous" and substituted the term "defect." Thus, the jury instruction

and the criterion used by the product safety engineer were that a

defective design is a design that subjects a user or bystander to a

"unreasonable risk of harm" from the reasonable and foreseeable use of

a product. However, on March 23rd 1976, a California Appeals Court, in

Foglio V. Western Auto Supply, 56 C. A. 3d 470, another lawn mower case,

ruled that the unreasonable risk of harm instruction was erroneous,

prejudicial, and in contravention of the common law of California. Only

the term "defect" was to be used. Thus, the level of risk that can be

tolerated has and is being lowered. So the safety engineer must have a

better understanding of low risk and rare event hazards, a broader

understanding of design alternatives, less reliance on customary practices

of the industry, and better insight into what those sitting on juries

would believe to constitute a defect and unacceptable risk. Thus, the

law is changing the rules of the game for safety engineers, and those

safety engineers who understand this fact of life have a new blatant thirst

for a broad range of safety research data, analyses, and conclusions.

Since any safety engineer must expect, sometime during his professional

career, to testify in court proceedings, he should also have some understanding

of what is meant by such terms as assumption of the risk, contributory

52
negligence, and conparative negligence. But, for assumption o£ the

risk, do we have very much research that will help us really define what

it is when a person "voluntarily" and "unreasonably" subjects himself to

a "known" danger, with an "appreciation" of the "amount of danger?" For

contributory negligence, exactly what constitutes a failure to use

"ordinaiy care" for the protection of one's own safety? Do we understand

why some people continue to operate or use a product after "discovery"

of its "defective condition?" Do we have a rationale basis for allocating,

in percentages, the degree of "human fault" under comparative negligence

determinations now being made by juries? The behavioral sciences could

contribute a great deal if they could rigorously explore, carefully define,

and illuminate risk-taking behavior in terms and circumstances useful

to lawyers, judges, juries, industrial managers, and safety engineers

in connection with the "recognition" and "appreciation" of "danger," failure

to exercise "proper care" for personal safety, and the assumption of risk

in varying situations and by groups varying in age, intelligence,

education , etc

.

This is a worthy field of endeavor and one that could greatly

influence the field of safety. Worthwhile results would command the

attention of a widespread group of people, since the forcing function may

be the very economic survival of otherwise viable industrial and commercial

enterprises . The imperative lies in our future generations , who should not

be needlessly maimed and crippled in the fashion of our current generations

who are forced to work, travel, and live in an unconscionably unsafe

environment

.

53
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A,
METHODS FOR STUDYING COMPLEX HOMEMAKING TASKS

Rose E. Steidl, Ph.D

Cornell University

ROSE E. STEIDL, is professor and chairman,

Department of Design and Environmental Analysis

in the College of Human Ecology at Cornell University.

Dr. Steidl has long been involved with research

on household tasks and the design of home work

environments. Her work is reflected in numerous

technical and consumer oriented publications.

Among these is the book Work in the Home (John Wiley

and Sons, 1968, co-authored by Ester Crew Bratt on)

.

Although Steidl 's work has not been directly

concerned with accident or safety research, the

methods she has employed and discusses in the

present paper, do have immediate application

to such research. Of particular interest is the

use of memo motion film techniques in observational

studies

.

Introduction

Task complexity is a comparatively unstudied area in home management

in relation to safety, yet information about complex tasks may contribute

to accident prevention. In this paper, I include some information about

complex tasks and present two methodological approaches \\rhich have been

used and may serve as a bench mark for further work.

Homemaking work is an ever present and changing problem. Some changes

come from within the home- -from the homemaker herself, the family, the tasks.

Other changes come from outside the home- -the goods and services available,

technological developments and shortages, the community, and the weather, for

instance.

Even though homemaking work has many changing aspects, there is often a

certain amount of sameness that leads to many routines and almost surface

attention while doing the different tasks. The worker's mind is not

completely occupied, but not free enough to let the homemaking task become the

secondary task for very long.

Homemaking includes many tasks with contrasts in characteristics

.

Some tasks are physically demanding, others more thought demanding; some

are judged large, others small; some discontinuous, others continuous;

some liked, others disliked; some are simple, others complex. We do not

know enough about task complexity. For example, does complexity come from

within each task, from the coordination of tasks within the heme, from

the coordination of tasks between the home and outside it , or from the

context within which the tasks are done?

55
Some of our data suggest that one source of complexity is from

combining and fitting tasks together (Steidl, 1975a). Managing a home

requires coordinating both a variety of activities and the parts of

each activity. Many tasks encompass time and location variables;

the worker controls some of the discontinuity of action, and events

external to the situation may affect further the stops and starts.

However, some of the intermittency of action is inlierent in the nature

of the task. The processing may continue without the worker being present,

thus permitting the worker to change to another activity (Steidl, 1963a;

Steidl and Bratton, 1968).

Machine washing of laundry can be used as an example of intermittency

of action that is inherent in the nature of the task. A natural division

of action occurs after the machine is loaded and the washer started.

Washing time must elapse before the next part of the task can be done,

and the worker need not be present during that time interval . In meal

preparation, much of the work may also be intermittent. For example,

baked potatoes cannot be produced by one continuous action; work is

necessarily interrupted while the potatoes bake, the worker, therefore,

has active and inactive work periods for the job of baking potatoes.

This characteristic of intermittent action on a task is not unique

to homemaking tasks, and it is not a particularly difficult concept to

comprehend. What is probably difficult is to identify all of the

implications, and at this workshop, to consider the importance for

safety. Both the amount of shifting from one activity to another and

the number of activities being carried on concurrently may be closely

related to fatigue, to attention demands. Other considerations are the

number of changes of location, the duration of action in the various work

periods, the tasks done together, and the order of doing them.

We have used memomotion film records of meal preparation and cleanup

to study the continuity of action on each menu item or "job" and the

following graphs* provide timing and changes of location data from one

set of case studies in which the working conditions were varied but the

menu remained constant (Steidl, 1957).

Memomotion film analysis

A memomotion film is a motion picture film exposed at less frequent

intervals than the common rate of 16 frames per second in micromotion

films. Usually, memomotion films are made at the rate of one frame per

second, but occasionally at 10 frames per second. Each frame is a picture

exposed for a fraction of a second. This technique was developed almost

*Ed. note: Graphs and other figures referenced in the text are presented

at the end of this paper.

56
30 years ago, in 1947, by Dr. Marvin E. Mindel, an industrial engineer at

Purdue University. Mrs. f^ry Koll Heiner at Cornell University recognized

the potential for studying work in kitchens and we adapted the technique

to our purpose. I brought several films with me and will use them to

demonstrate some of the methods of analysis and characteristics of tasks.

The memomotion films, of course, do not provide a complete record since

15 out of every 16 frames of the film are missing. The action is jerky,

like the old Charlie Chaplin films, rather than continuous and smooth.

For the most part, the missing detail has not been a problem. Analysis is

easier, however, when a brief written record is made concurrently with the

film record; the analyst then has a faster and less tedious job of recording

data. Whether the same thing is true with the more sophisticated recording

systems available now may be a question you would discuss later.

We have analyzed memomotion films for various kinds of information:

"to determine what activity was being done, how it was done, what

was used, who was doing it, who else was present, and exactly where it took

place. The duration of the activity and the sequence of events can also

be determined.

"Time can be determined most directly by obtaining a count of the

number of frames on the film for the unit of activity being studied. When

one frame of film is briefly exposed every second during the observation

period, the number of frames counted can be equated to the number of seconds.

Reference to a clock in the camera field may also provide information about

the passage of time," (Steidl, 1963b, page 14).

A film record has a number of advantages over a paper and pencil record

of an observation: it provides a fairly permanent record; it can be analyzed

for various types of information; observations and analyses can be verified;

and it permits reviews of activity which may suggest additional information

that will contribute to the solution of the problem or help identify other

problems

.

A memomotion film also has these advantages

:

. The analyst has less film to review, since it is a more condensed

record than a micromotion film.

. Undesirable conditions may be emphasized, since motions are jerky

and accentuated.

. It is not necessary for an observer to be present during a trial

to record what a subj ect does

.

. An hour's activity can be reviewed at normal speed of 16 frames

per second in four minutes , thus permitting a quick overview of

a trial.

57
I

. It is well suited to problems that do not require as detailed analysis

as permitted by a micromotion rate of 16 or more frames each second,"

(Steidl, 1963b, page 14).

Of the disadvantages of any film record, the one that is unique to

memomotion films stems from the intermittent record, i.e., action is missing

during the unrecorded periods. Of course, some information may be missing

in any film because the worker's back is to the camera, thus concealing the

activity. However, when data are recorded also by an observer concurrent

with the filming, the problem may be eased.

Next, I want to present several examples of the kinds of data from memomotioi

film records of a complex task- -meal preparation- -and films from two of our

studies

.

Since the data from the films and observations are objective, some

means of obtaining the person's evaluation and perception of the activity

and situation should be used to help interpret the objective data. For

instance, effort ratings have been correlated with total number of centeruses (or trips) , time at each center (or work station) , and the over all

assessment of different arrangements (Steidl, 1960).

Interview method and continuity of action

Data from personal interviews have also been used to study continuity

of action in household work. As you would expect, the information is

ordinarily at a much grosser level than that from films. For instance,

interviews asking for recall of the preceding day's activities and the

estimated time for each activity gave us knowledge of the number of blocks

or units of activity, the duration of each, the sequence of activities,

and the variety (Steidl, 1963; see also Steidl and Bratton, 1968). From

these data we obtained descriptive information pertaining to continuity of

action. The number of blocks of activity averaged 20 per homemaker and

two-fifths of the blocks of activity continued for less than 30 minutes;

one-third of the homemakers reported actiyities in three activity areas

(such as food, clothing, family) and another one- third reported activities

in four activity areas.

Our experience indicates that respondents can reconstruct their timeuse, and especially when the query concerns the last 24 hours rather than

a part of the last 24 hours. The sequential listing of activities and

associated time periods lends itself to several kinds of analyses, including

those indicated.

Complex homemaking tasks - interview method

Another approach to studying complex homemaking tasks besides the

filmed observations is the personal interview, using questions about the

cognitive factors of attention, judgment, and planning. Explanatory

I

I

58
information can be obtained about the functioning of each cognitive factor,

difficulty factors, and task preferences, as well as ratings for complexity,

difficulty and preference. Three journal articles provide details of the

methodology and the results from intensive interviews with a selected

population of young wives (Steidl, 1972; Steidl, 1975a; Steidl, 1975b).

The information that follows is based on those articles.

Open-ended questions were used and many could be used or adapted in

further studies. Two questions about homemaking tasks in general

elicited a range of information and provided rich insights into the

concept: "What makes homemaking tasks complicated?" "What makes homemaking

tasks uncomplicated?" Following this, the respondent nominated tasks

high in attention and others low in attention and answered open questions

including these:

-"Why do you think (name of task) requires a great deal of attention

(or judgement, or planning)?" or, "Why do you think requires

very little attention (or judgement, or planning)?"

"Are there any things about your work situation or where you do this

task that make the work more difficult?" and "Are there any things

about your work situation or where you do this task that make the

work less difficult?"

-"What do you like about this task?" "What do you dislike about this

task?"

The coding of the responses was, of course, time consuming. The

diversity of responses was impressive. Some of the diversity came from

the variety of tasks nominated. One advantage of the open-ended questions

was the richness of the information. With this as background, a more

structured interview schedule could be developed; broad categories might

be used, followed by a request for more specific information if appropriate.

For instance , the wives ' explanatory information about the high cognitive

factors eiq)hasized the content of the work, and especially quality and

quantity considerations, timing requirements, and process or procedure

activities. Some wives also noted aspects of the environmental context -- the house, community, and family.

MDre specifically, the quality and quantity considerations often

concerned quality, especially aesthetically pleasing results such as

color, flavor, things going together; also variety of products, interesting

products; growth, health, diet, and nutrition factors; attending to

temperature settings to obtain a quality product; and judging the

sturdiness and durability of items . The quantity considerations often

involved judgments about how much to do or use.

59
The timing considerations concerned careful timing required; decisions

about when to do the task; judging the amount of time needed; and the

time squeeze. Some noted also timing tasks to prevent accidents or

provide safety for their children.

The liigh cognitive tasks also required thought about the process or

procedural activities such as how to proceed with the task: attending,

judging, or planning how much, when, what to use or substitute; and the

preparatory work and organizing work required.

The family and human relations involved also were among their concerns:

pleasing self and others; taking care of the preferences and needs of

others. The age of the child, the schedules of the child, wife, and husband

for work and other activities were other considerations..

The preceding examples are some of the more frequent kind of

responses in the wives ' explanations of high cognitive tasks . Our data

provide information about the dimensions of complexity of tasks and of

tasks that are not complex. The wives' responses also point up the impact

of their situation when they are tight on time and of the social and physical

setting in which tasks are done.

The relationship between difficulty factors and complexity should

not be overlooked. The high cognitive tasks were rated almost equally

as easy and difficult. The homemakers identified factors making tasks

both more difficult and easier to do. Since about half of each set of

reasons concerned the quality of the physical environment, it should be

included in further studies of task complexity.

Conclusion

Two methods of studying complex homemaking tasks --the interview

and memomotion film analysis --provide different kinds of information about

tasks and the situations in which tasks are done. I^ny homemaking tasks

encompass time and location variables; the worker controls some of the

discontinuity of action, the process determines seme, and events external

to the situation may affect further the discontinuity of action. Since

action is intermittent, coordination of tasks is needed. Social interaction makes additional demands on the worker's attention. The context

within which tasks are done, such as inadequate time, multiple task

performance, equipment breakdown, and poor quality of supplies, may

contribute to difficulty or complexity of task. The nature of the work

and the setting in which it is done are both important in studying

task complexity.

60
Percent of center-uses

N = 113

Percent of time at centers

N = 4904 seconds at centers

FLOW OF WORK FOR PREPARATION AND CLEANUP OF ONE DINNER

The solid portions in each column represent action on a given job for the

meal, the blank portions no action. Study of the graphs shows:

. the number of different times a job received attention (meat—8 times);

. proportion of center-uses during each attention period;

. proportion of time during each active and inactive period;

. action on several jobs during some attention periods (meat, potatoes, gravy);

. sequence of work (first job—dessert; next—potatoes; dessert; meat;

cleanup ; etc . )

Discontinuity of action during preparation and comparatively short work

periods on each job were common for this menu (ground beef patties; mashed

potatoes; pan gravy; tossed vegetable salad; milk, water, coffee; brownies).

Source: Steidl, Rose E. (1957) "Effects of Multiple Water and Drainage

Facilities on Work Involved in Family Meal Preparation and

Cleanup," Ph.D. thesis, Cornell University, Ithaca, New York.

61
(1) W P- O )-l Q) 3 iJp>^'da)<i)(U u C

fli iJ(TjiHa3U-(^'H4-)(U

FLOW OF WORK FOR PREPARATION AND CLEANUP OF ONE DINNER

The solid portions In each column represent action on a given job for the

meal, the blank portions no action. Study of the graphs shows:

. the number of different times a job received attention (meat—8 times);

. proportion of center-uses during each attention period;

. action on several jobs during some attention periods (meat, potatoes, gravy);

. sequence of work (first job—dessert; next—potatoes; dessert; meat;

cleanup; etc.)-

Discontinuity of action during preparation and comparatively short work

periods on each job were common for this menu (ground beef patties; mashed

potatoes; pan gravy; tossed vegetable salad; milk, water, coffee; brownies).

Source: Steidl, Rose E. (1957) "Effects of Multiple Water and Drainage

Facilities on Work Involved in Family Meal Preparation and

Cleanup," Ph.D. thesis, Cornell University, Ithaca, New York.

62
Number of trips into the kitchen

(From memomotion films of four meals in two

homes, before and after adding functional

storage devices, 1959)

Family C Family J

Before After Before After

Number of trips into kitchen

Homemaker 14 22 4 12

Helpers

Work only 13 20 20

Visit only 1 10 11

Work and visit 1 1 13 7

Visitors 8 18 3

Total 36 42 50 50

Steidl, 1961b

63
Duration o£ periods in and out of the kitchen

(From memomotion films of four meals in two homes, before

and after adding functional storage devices, 1959)

Homemaker Helpers Total

Duration Before After Before After Before After

Tn Tn111 Tn Out In Out In C\i UUti-f- T-n r>i in uut

Seconds Family C: number of periods

1-29 8 11 10 16 11 4 1 19 15 11 16

oU- by i 1 0

•73 1 2 1 2 3 7 3

60 and over .5 6 2 5 1 7 5 6 1

No data 2 3 3 1 5 4

Total 1 A 14 14 22 22 14 14 2 2 28 28 24 24

Family J: number of periods

1-29 1 1 1 4 31 18 27 16 32 9 28 20

30-59 3 3 5 7 5 6 5 7 8 9

60 and over 3 8 1 7 12 6 9 10 12 14 10

No data 3 4 6 7 9 11

Total 4 4 12 12 43 43 38 38 47 47 50 50

Steidl, 1961b

64
65
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66
67
FIGURE 1. WHAT MADE WORK...*

X 60 50 40 MORE DIFFICULT

30 20 10 0

llllllllllllllllllliilllllllllllllllllllllll

llllllllllllllllllllllllll

llllllll

HOUSING AND FACILITIES WITHIN DWELLING

WORK CONTENT

FAMILY AND

COMMUNITY

LESS DIFFICULT

0 10 20 30 40 50

llllllllllilllllilllllllllllllllllllllllllllll

60 %

1 1

lllllllllllllllllllil

Key:

For 622 tasks high in attention, judgment or planning

D% of 1,095 responses B% of 1,033 responses

For 414 tasks low in attention or jurigment 11% of 670 responses ||% of 701 responses

|i;j;;Hl} AFFECTIVE AND

III COGNITIVE CONSIDERATIONS

llllllll

nil

i

FIGURE 2. WHAT WAS IT ABOUT THE HOUSING AND FACILITIES THAT MADE WORK.

X SO 40 30 MORE DIFFICULT20 10 0

lllllllllillll

LESS DIFFICULT

0 10 20 30 40

piiiHIIinHnnl HOUSING TYPE AND

llllllllll STRUCTURAL QUALITY

50 X

llllllllillllllliilll1 i H SPACE, ROOMS

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

1 i llllllllllll

llllllllllllllllllllllllll AND FURNISHINGS

tjjjjiiHniiiinHiiiiiyniiiinyyyyin^ equipment

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii and supplies

tiijiHiyjiiiiiiiiil work surface

lllllll AND STORAGE SPACE'

Amount

Design

Location

Temperature, light, ventilation, sound, safety Housing quality and age

Stairs and apartment level Housing type and renting or owning

Total amount Number of rooms

Floor plan and room design

Pleasantness

Design and quality

Availability Location of equipment and task

Key: For 622 tasks high in attention, judgment or planning E3% of 580 responses H% of 506 responses

For 414 tasks low in attention or judgment 11% of 361 responses ||% of 40S responses

* According (o the responses o( 208 homemakers In Ithaca, N.Y., and vicinity, 1%7

Steidl, 1972 (Based on Tables 2 and 3)

68
REFERENCES

Steidl, Rose E.

1957. Effects of Multiple Water and Drainage Facilities on Work

Involved in Family Meal Preparation and Cleanup. Thesis

for degree of Ph.D., Cornell Univ. 378 pp. (Microfilm.)

1960. Supplementary Sinks in Home Kitchens. Cornell Univ. Agr.

Exp. Sta. Memoir 374. 19 pp.

1961a. Work Before and After Addition of Functional Storage Devices

in Home Kitchens. Cornell Univ. Agr. Exp. Sta. Bui. 969.

(out of print) 23 pp.

1961b. Family in the Kitchen. Research Report 6. Dept. Household

Econ. and Mgmt. , N.Y. State Coll. of Home Econ. , Cornell

Univ. 18 pp.

1963a. Continuity of Household Work. Cornell Univ. Agr. Exp. Sta.

Memoir 383. 20 pp.

1963b. Research Methods for Study of Human Costs of Household Work:

Development and Use at Cornell University. Cornell Univ. Agr

Exp. Sta. Bui. 988.

1972. Difficulty Factors in Homemaking Tasks: Implications for

Environmental Design. Human Factors , Vol. 14, No. 5

(October 1972) , 471-482.

1975a. Complexity of Homemaking Tasks. Home Economics Research

Journal, Vol. 3 (June 1975) pp. 223-240.

1975b. Affective Dimensions of High and Low Cognitive Homemaking

Tasks. Home Economics Research Journal , Vol. 4

(Deconber 1975) pp. 121-137.

Steidl, Rose E. and Bratton, Esther Crew

1968 Work in the Home. New York: John Wiley and Sons, Inc.

69

DATA COLLECTION FOR HAND TOOL INJURY:

AN APPROACH

M.M. Ayoub, Ph.D. , P.E.

Texas Tech University

Jerry Purswell, Ph.D.

University of Oklahoma

John Hicks

Cities Service Oil Company

M. M. Ayoub, is professor of Industrial

Engineering and Biomechanical Engineering as well

as Director, Institute of Biotechnology at Texas

Tech University. His research interests center

around ergonomics , with particular interest in

biomechanics and work physiology.

The paper presented here, co -authored by

Jerry Purswell, University of Oklahoma, and

John Hicks, Cities Service Oil Company, presents

an ergenomic approach to data collection for the

study of hand tool injuries. Ayoub et al consider

the worker, the tool, the task, and work practices

in their determination of required information

and the development of a reporting procedure for

hand tool injury.

INTRODUCTION

The term hand tool used in this paper refers to any of the wide range

of hand held instruments used to perform a given task. These hand tools

can be powered either by muscular exertion or by outside source, but all

are held and manipulated by the human hands in a man- task-environment

system consisting of the worker himself, the tool used, and the environment

in which the work is performed.

A hand tool should be and is designed to extend the human physical

capabilities in performing an activity, but at the same time these tools

have caused injuries to the user as well as to other individuals in a

variety of ways. As a rule these accidents are often attributed to

negligence or bad luck, but rarely, if ever, have they been examined to

identify the real mechanism of injury to eliminate or at least expose it

in order to prevent repeated occurrences . Only in recent years has an

effort been made in this country to examine accidents with more interest

than just score keeping. This is partially the result of the Occupational

Safety and Health Act of 1970.

71
Data published by the National Safety Council (1972, 1973) indicate

the severity o£ hand tool injury problems. Hand tool injury data accounts

for 6% of all compensible injuries in 1971 and 1972. Due to the high

incidence and high cost of tool injuries, it is imperative that efforts

be initiated to investigate and attempt to eliminate the causes of these

hand tool injuries. Such action would certainly decrease the frequency

and severity of the hand tool injuries.

Purpose

The purpose of this paper is to show an Ergonomic approach for the

collection, and analysis of information on hand tool injuries and illnesses

and to test such a system of injury collection and analysis on a group of

accident cases at Tenker Air Force Base. This system is presented in

detail in a later section.

Summary and Evaluation of Injury Statistics

Based on the literature search compiled by Ayoub, Purswell and Hoag

(1975) , it was clear that the injury data available are related primarily to

incidents of a fatality or disabling injury which results from hand tool

use. Additional data are available from some states which relate the

incidence of injury to a particular type of hand tool. However, data are

not generally available to relate the incidence of injury to a particular

hand tool and mechanism of injury. Of course, the mechanism of injury

can, in some cases, be inferred from the statistics available for the type

of hand tools such as knives , but more data are needed to relate the

incidence to the mechanism of injury.

For the data available there are differences in criteria used to

pay compensation for hand tool injuries, for instance, an injury may

be classified as a disabling injury in California if it results in

absences from work one full day, or shift, beyond the day of injury,

while the comparable period in New York is seven days. These differences

in criteria make it difficult to make comparisons between the available

injury data. The following sections contain a summary of the data

available on injuries resulting from hand tool use.

A. Hand Tool Injuries as a Proportion of All Compensable Injuries

The National Safety Council (1973, 1972) published the data shown in

Table 1 on the source and cost of compensable work injuries as reported by

state labor departments in the U.S. for the calendar years of 1971 and

1972.

It can be seen that hand tool injuries accounted for six percent of

all injuries and the average cost of compensation only for each accident

was $740 in 1971 and $850 in 1972. The relative position of the various

injury sources as a percentage of all injuries did not change from 1971 to

1972, but the average compensation costs did increase approximately

15 percent for each injury source. Comparable data for a calendar year

1973 was not published in the 1974 edition of Accident Facts.

72
TABLE 1

SOURCE AND COST OF COMPENSABLE WORK INJURIES

Average

Percent of Compensation

All Cases Costs per Case

Source of Injury 1971 1972 1971 1972

Handling objects, manual 23 23 $ 990 $1,140

Falls 20 20 1,470 1,690

Struck by falling, moving

ODj ecus 1 A / oU oDU

Machinery 10 10 1,110 1,280

Vehicles 7 7 1,570 1,800

Stepping on, striking against

obj ects 7 7 480 550

Hand tools 6 6 740 850

Other 13 13 1,182 1,350

Accident Facts, 1972 and 1973 editions.

73
Data published by the State of New York for the period 1966 through

1970 (1972) show that injuries resulting from hand tool use account for

7.0 percent of all injuries and 4.9 percent of the compensation awarded

accident victims. The average cost of compensation per hand tool injury

was $1,305. The data available from New York were summarized for the fiveyear period but no annual information was available to determine any time

trends

.

The State of California published information annually on work injuries,

so it is possible to infer the time trend of injuries resulting from hand

tool use as shown in Table 2.

The data in Table 2 indicate that hand tools were involved in

approximately 9.0 percent of all disabling injuries and 1.9 percent of

fetalities over the six-year period of 1967-1972. There is also an

indication that the trend of hand tool injuries is upward over the last

three years of data (1970-1972)

.

Data were not available from California on the average compensation

cost of a hand tool injury.

Table 3 presents data for the State of Ohio, showing the percentage

of fatalities and injuries produced by hand tools for all compensable

injuries

.

A comparison of these various data sources indicates differences

from state to state, but in general, it can be concluded that injuries

resulting from hand tool use account for 5-10 percent of all compensable

injuries

.

B. Injuries Resulting from Powered Versus Nonpowered Hand Tools

The data available from New York, California, and Ohio for hand tool

injuries include a number of subclasses, permitting an analysis of powered

versus nonpowered hand tool injuries. Table 4 presents data for

California showing powered hand tool injuries as a percentage of all hand

tool injuries.

Table 5 presents data from the State of Ohio for powered hand tool

injuries as a percentage of all hand tool injuries.

Data from the State of New York for 1966-1970 indicate that 21.1 percent

of hand tool accidents were produced by powered hand tools , and that the

average compensation cost per case was $1,610 compared to $1,221 per case

for nonpowered hand tool accidents. Considering the data from these

three states as typical, it can be stated that powered hand tools account

for 21-29 percent of all hand tool injuries. It may also be inferred from

the New York data that compensation for a powered hand tool accident will

be an average of approximately $400 more than for a non-powered hand tool

accident

.

Referring to Table 1 presented earlier, it may also be observed that

the cost of a hand tool compensation claim in New York was almost twice

the national average.

74
TABLE 2

FATALITIES AND DISABLING INJURIES RESULTING FRCM HAND TOOLS

TOTAL USE IN CALIFORNIA FOR THE PERIOD 1967-1972

AS PERCENTAGE OF ALL INJURIES

Year

Hand Tool Fatalities

as Percent of All

Fatalities

Hand Tool Injuries

as Percent of All

Injuries

1967 1.5 8.7

1968 1.4 9.0

1969 2.0 8.8

1970 2.1 8.7

1971 1.5 9.0

1972 2.8 9.4

TABLE 3

FATALITIES AND DISABLING INJURIES PRODUCED BY HAND TOOLS

AS A PERCENTAGE OF ALL COMPENSABLE INJURIES

FOR THE STATE OF OHIO

Year

Hand Tool Fatalities

as Percent o£ All

Fatalities

Hand Tool Injuries

as Percent of All

Injuries

1969 Not Available 4.7

1970 1.0 4.8

1971 2.1 5.0

1972 1.2 5.1

-1973 Not Available 5.5

75
TABLE 4

INJURIES RESULTING FROM POWERED HAND TOOL USE AS A PERCENTAGE

OF HAND TOOL INJURIES FOR STATE OF CALIFORNIA

Year Percentage

1967 26.6

1968 27.4

1969 28.5

1970 28.2

1971 25.1

1972 29.1

TABLE 5

INJURIES RESULTING FROM POWERED HAND TOOL USE AS A PERCENTAGE

OF ALL HAND TOOL INJURIES FOR STATE OF OHIO

Year Percentage

1969 22.8

1970 20.6

1971 24.2

1972 23.1

1973 21.6

76
C. Injuries Related to Specific Type of Hand Tool Use

The data from New York, Ohio, and California were analyzed to obtain the

percentage of total hand tool injuries contributed by each type of hand tool.

Some problems exist in obtaining comparable classifications of injuries by

type of hand tool in each state, but these were generally overcome by

rearrangements of the detailed accident data where necessary. Table 6

presents the data for hand tool type versus percentage of total hand tool

injuries for New York, Ohio, and California.

It can be seen from Table 6 that there is very good agreement among

the three states over several years of data on the 1, 2, and 3 relative

ranking of hand tool injuries produced by knives, wrenches, and hand

hammers . There is also good general agreement on the relative ranking of

the frequency of injury for the other hand tools within the list.

Exceptions to this general agreement in ranking are where the basic data

do not permit data tabulation on a comparable basis for a particular tool

type such as a bar or pneumatic tool. The data in Table 6 can be considered

to represent one type of priority listing for defining research requirements

to inprove the safety of hand tool use. Of course, it would be very

desirable to have some estimate of the relative exposure of a worker in

using each type of tool in order to more effectively plan a research

program, but such data are unavailable.

Another consideration in establishing research program priorities is

the cost of a given type of hand tool injury as compared to the frequency

of injury. As stated earlier, the only data available which relate

compensation costs to a specific hand tool injury type is New York state.

Table 7 presents these data.

It can be seen from Table 7 that injuries resulting from the use of

shovels and spades result in the highest compensation costs of all hand

tools, while only ranking fifth in number of injuries among all hand tools.

Similarly, injuries resulting from the use of knives rank fourth highest

in compensation costs while ranking number one in frequency of injury.

Such differences in incidence of injury versus condensation cost of the

injury must be taken into account in the establishment of research priorities.

In order to consider the development of control measures to prevent

hand tool injuries, it is necessary to have an understanding of the

mechanism of injury as noted earlier in this paper. The most complete

data available in this case is from the State of Ohio. Table 8 presents

a conpilation of data for various hand tool categories where the type of

accident, nature of injury and part of body injured are shown. The

following comments for knife and wrench injuries illustrate how the data

in Table 8 may be used to better understand the mechanism of injury:

(1) Knife - lacerations account for 89 percent of all injuries, as would

be expected. Most of these lacerations occur on the fingers and

hands

.

77
TABLE 6

PERCENTAGE AND RELATIVE RANK OF SPECIFIC HAND TOOL

INJURIES AMONG ALL TYPES OF HAND TOOL INJURIES FOR

NEW YORK, OHIO, AND CALIFORNIA

Percentage and Rank of

Hand Tool Injuries

New York Ohio California

Type of Hand Tool 1966-1970 1969-1973 1967-1972

% Rank % Rank %

' Rank

Knife 17,0 1 17.7 1 17.7 1

Wrench lU. o L il . o Z z

Hand hammer 9.2 3 7.1 3 7.1 3

Nozzle/hose 3.9 7 3.5 6 5.0 4

Shovel/spade 4.2 6 5.0 4 4.2 5

Bar 6.2 4 1.4 10 3.5 8

Scissor/shear 1.8 11 0.8 12 3.3 9

Power drill 3.2 10 3.7 5 2.8 10

Power saw 3.4 8 3.3 7 3.8 7

Grinder 1.0 12 1.9 9 2.5 11

Sledge 3.3 9 3.3 7 2.1 12

Pneumatic tools 5.1 5

0.9-^ 11 4.0 6

Some pneumatic tool injuries classified in non-hand tool

categories

.

78
TABLE 7

TOTAL COST AND COST PER CASE FOR SPECIFIC

TYPES OF HAND TOOL INJURIES FROM STATE OF

NEW YORK FOR PERIOD 1966-1970

Total Cost o£

Type of Hand Tool Compensation Cost per Case

Shovel/Spade $4,199,400 $3409

Wrenches 4,037,100 1260

Hammer 3,217,300 1178

Knife 2,991,500 595

Bars 2,732,400 1483

Pneumatic 2,423,600 1606

CIlJ ^pdcro ^V-* tl \^ 1 943 700 1967

Hoses/Nozzle 1,925,100 1655

Power Saw 1,676,400 1647

Power Drill 1,351,000 1434

Scissors/Shears 660,100 1211

Hook 59Z,900 1808

Power Grinder 324,300 1150

79
(2) Wrench - the most frequent type of accident is slipping (without

falling, which is another category of accident) or overexertion.

Injuries where a person is struck by a moving object are also

important. The most common type of injury is a sprain or strain,

with contusions being the second most frequent type of injury.

Injuries to the low back occur most often, with the arms, hands

and fingers also becoming involved in a significant number of

wrench accidents.

These two exanples illustrate the type of information contained in

Table 8 for each type of hand tool. Such information is not detailed as

could be desired to fully understand the circumstances of each type of

hand tool accident, but it does provide the best basis available for

understanding hand tool accidents sufficiently to outline a program of

research in the area. The objectives of this program of research will be

the collection of additional data which can be used to design safer hand

tools and workplaces

.

The following section provides an analysis of the requironents for

injury -relating data, given the type of information which is currently

available for hand tool injuries and taking into account the needs for

additional data before safer hand tools , workplaces and work practices can

be designed.

Requirements of Injury-Relating Data

The statistics available today on injuries and illnesses caused by the

use of hand tools are inadequate for an evaluation of the characteristics of

the tool design, user practices, task design, and the worker which

contributed to an accident or illnesses . Available information can be

divided into three classes : (1) statistical information on the number of

injuries by industry, age, severity, cost, etc., (2) anecdotal accounts

published in safety or trade journals whose intent is to promote safety,

and (3) medical articles concerned with the treatment or description of

the injury or illness.

The type of statistical information available has been presented in

the previous sections. It was noted that the data can only be used to

generally indicate the agency of injury for a specific hand tool, leaving

unanswered many questions about the mechanism of injury. Both anecdotal and

medical reports have purposes which are not necessarily consistent

with resolving tool design problems. Anecdotal accounts of injuries

typically emphasize the need for better work practices, maintenance of

tools, and using the correct tool for the job. Seldom is any information

given on the number of workers exposed to the hazard, the number of accidents

which occurred or factors which may have indirectly contributed to the

situation. Medical accounts of injuries are primarily concerned with

treatment of the injury with only a brief description of how the injuries

occurred. Medical accounts of illness are more informative of variables

which influence the condition and frequency of occurrence in the population,

but frequently lack quantitative information on the tools and workplace

in which the illness or injury developed.

80
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81
This section of the paper discusses the general requirements o£ data

collected to provide the information basis for assessing the importance

of characteristics of the worker, the tool, the task and the work practices

in the occurrence of injuries and the development of occupational illnesses.

A. Description of Data Requirements

An outline of the requirement of injury-related data is shown in

Figure 1. Notice that the injuries and illnesses are categorized by

several factors. For each accident or illness a complete description of

the conditions relevant to the situation are described. The system

characteristics of the worker, tool, task and work practices are all

considered in terms of the injuries and illnesses associated with these

factors. The system characteristics such as the worker, tool, etc.

are further subdivided into the individual factors associated with each

major characteristic.

Through a planned, coordinated set of studies, the importance of

these system characteristics to the design of the various types of tools

can be evaluated. Basically two types of information are required:

(1) Detailed information on actual injuries and illness to assess the

causes, and (2) studies of the impact of specific attributes of the work,

tool, task, or work practices on the occurrence of accidents and illnesses.

The first category of information has to be collected in industry, while

the second category of information can be developed in a laboratory or a

combination of laboratory- field studies. The sections which follow describe

the information required in each of the categories

.

B. Information about the Worker

The information required in this section is descriptive information

about the worker which may permit an evaluation of which characteristics

of the worker directly or indirectly contributed to the injury or illness.

These data are required based on the assumption that all the relevant

antecedents may not be recognized by the safety or medical personnel

writing the report, and it is possible that the relationship between the

antecedents and the accident or illness may not be understood by the

researcher in the area. Briefly the areas of information required are:

(1) Anthropometry- -A complete description of the size of the members of

the body which are used to control the tool and the angles between the

links of the body when the tool is operated. Special attention must

be given to describing the position of the hand.

(2) Motor Skills - -A profile of motor skills of the workers to obtain any

relationships between these skills and accidents. For example, Welford

(1958) made the observation that accident prone workers have better

than average motor skills , but in young workers a combination of too

much confidence in their motor skills and inexperience reduced their

ability to recognize a dangerous situation and led to the more frequent

occurrence of accidents. This observation requires verification on a

U.S. population of workers.

82
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83
(3) Sensory Skills and Sensory Feedback- -A profile is needed of the

acuities of the visual, aural, tactal and proprioceptive senses and

the ability of the worker to use this information.

(4) Psychomotor Skills - -Measures of the ability of the individual to combine

mental processes with motor processes will provide the opportunity

to assess the importance of skills such as hand-eye coordination on

the occurrence of injuries.

(5) Training and Experience- -Training and experience will be an indicator

of the knowledge the individual has of the tool , the correct methods

of using the tool and the potential dangers associated with its use.

One basic assumption has to be made in using experience as a measure

of knowledge. This assumption is that the opportunities for learning

are directly proportional to the years of experience, i.e., that with

an increased number of years of experience more learning experiences

will be encountered instead of repeating the same learning experiences

.

A measure of the value of training and experience on the rate of

occurrence of injuries and illnesses will then result.

Some of the information in these five categories can and should be

collected on the job at which the injury occurred or the illness developed

while other information will have to be collected in research projects.

For example, the cost of periodical surveys of the motor skills, sensory

skills and psychomotor skills of a large segment of a company's work

force cannot economically be justified as a routine procedure. Information

on the anthropometry, training and experience of a worker who is injured

or becomes ill would not be prohibitively expensive to obtain. Therefore,

research studies on selected populations of workers should be conducted to

evaluate the role of motor skills , sensory skills and psychomotor skills on

injuries and illnesses. Information on the anthropometry, training and

experience should be collected as routine investigative information whenever

a work related injury or illness occurs.

The measure of the attributes also determines the approach to collecting

the information. Measurement of the motor, perceptual and psychomotor skills

requires special training and equipment which is expensive. By comparison,

the cost of collecting anthropometric data and assessing the training and

experience level is considerably less expensive.

C. Information about the Tool

The information about the tool is subdivided into descriptive information

about the tool, its construction and how it operates and information

describing the physical coupling between the tool and its operator and

between the tool and workers in the immediate area surrounding the operator.

In the literature, the following reasons are frequently given for injuries

involving liand tools: (1) using the wrong tools for the job, (2) insufficient

or incorrect maintenance of tools, (3) using the tools improperly,

(4) ijnproper storage of tools, (5) defective tools and (6) failure to use

protective gear. But these causes are not discussed in terms of the

frequency of these factors being involved in accidents, e.g., no

information is presented on the percentage of hand tool accidents which are

caused by use of the wrong tool for the job.

84
In 1970, there were 1472 disabling injuries reported in California

which involved wrenches , but descriptive information was not provided which

will help reduce future injuries through avoidance of the hazardous

condition which contributed to the accidents. In 1972, 381 cases of

accidents involving wrenches were reported in Ohio. Of these 381 cases,

199 (52%) involved a slip or overexertion, 52 (14%) involved striking

an object or material and 116 (30%) involved being struck by a moving

object. It is possible to speculate on the causes of these accidents, but

no information is provided which could be used to test the hypotheses

.

Only by isolating the specific causes of accidents can progress be made

in reducing accidents and illnesses

.

The information which is required includes the attributes of the tool,

how it is used or misused and the contribution of the various aspects of the

job. Using information from anecdotal reports, knowledge of the design of

tools, statistical reports such as the Ohio data and experience with the

use of a tool, data collection studies need to be designed to obtain

information from accidents and illness cases which will lead to an

improved understanding of the role of tool design in injuries and illnesses.

D. Information about the Task

This category of information provides a description of the task and its

attributes which might contribute to the occurrence of accidents or

illnesses. Specifically included in this category are: (1) a description

of the workplace, (2) a description of the workpiece, (3) a description of

the environment and (4) a description of job requirements. The information

included in the description of the work piece will depend on the task, but

in general should include information to describe the position of the

worker while performing the task, facilities for proper storage of tools

and material, housekeeping practices and the relationship (spatial) with

other workplaces and/or machines . To describe the workpiece , information

on the operation performed on the workpiece and the material from which the

workpiece is constructed is required. Environmental information includes

the noise, illumination, radiation, vibration, heat (or cold) and air

quality at the workplace. Finally, the job requirements include information

on the forces, pressures, and job duration.

E. Work Practices

Included under this category is a description of the work practices

(i.e., methods and procedures) used to accomplish the job. These practices

might be a function of the individual worker, the company's policies or

equipment, or industry-wide methods. They might also be influenced by

government regulations, e.g., an OSHA regulation might determine a work

practice which influences the health or safety of the workers by altering

the method used in performing the job.

It can be seen from the foregoing descriptions of requironents for

injury-related data that a high priority must be given to developing a more

useful data base of liand tool injury and illness information. This data base

must contain sufficiently detailed information for the major hand tool

85
types to permit an analysis of the mechanism of injury. Control measures

can be successfully developed for hand tool injuries only after the required

data liave been collected. The most appropriate methods for collecting these

data, taking into account the costs and benefits involved, must be developed

in a research program.

The Proposed Approach

In order to develop an appropriate procedure for the collection of hand

tool injury data, the following steps were chosen:

1. Determination of the information required to describe the

accident and possibly to later estimate the contribution of

less obvious psychological and physiological factors.

2. Construction of a suitable form and reporting procedure.

3. Evaluation of several injury cases to establish the usefulness

and effectiveness of the information collected.

4. An iterative process of steps 1, 2, and 3; continued until the

procedure is proven to be suitable.

To determine the information required to identify the cause of an

accident, it is useful to consider an example. Consider a case involving

an electrician who cut the palm of his left hand while replacing some

wiring on a large aircraft. Many factors may be directly or indirectly

involved including workplace limitations, a faulty tool, inexperience in

a skill required by the task, and others.

To collect the needed information, the system characteristics approach

of Ayoub, Purswell and Hoag (1975) was employed. It covered all aspects of

the worker, the tool, the task. These are summarized in Figure 1.

Information collected about the worker is generally on anthropometry,

training, and experience. Measurements of motor skill, psychomotor skill

and sensory feedback ability are considerably more complex than collecting

the survey type information and would require a large segment of the worker's

costly time. For this reason, collection of this type of information should

be confined to selected populations of workers . Results could then be

related statistically to the large study population to assess their role

in causes of hand tool accidents . In this case , however , an effort was made

to test motor and psychomotor skills through administration of the One-Hole

test. (Salvendy, 1975) Designed to test the ability of an individual to

acquire a manipulative skill rapidly, it was used here to investigate

the effectiveness and practicality of such a test in this context. In

collecting injury data, a safety representative should, collect information

including name, age, sex, measurements of the hand and arm and their

positions during the task, and training and experience in this and similar

jobs, as well as conduct the administration of a motor skill and

psychomotor skill test in this instance. Data collected concerning the

tool should include all of the subheadings listed under tool in Figure 1.

86
To describe the task it is necessary to include a workplace

description, a workpiece description, a summary of task requirements;

meaning a description of necessary forces, torques, pressures and their

duration. For the example, the information required may be:

workplace - on left side of aircraft, 15 feet above ground on a

metal scaffold. Working at face level.

workpiece - 2 ft. x 3 ft. panel of several hundred wires.

task requirements - very light grip pressure and shoulder torque.

environment - 70 degrees, loud constant noise, clean area,

adequate lighting.

All of the relevant information concerning work practices should be

collected immediately from the individual involved, where possible, and the

supervisor. All practices (i.e., methods and procedures) used in the

performance of the task; whether individual, company policy or government

regulation must be included. The aircraft worker in the example might state

only that he used a square knot off center method of splicing and that no

other practices are applicable. For this study all of the work practice

categories were included in data collection efforts

.

In addition to the system characteristics associated with an accident

it is also possible that non-obvious stress factors contributed to the

accident. Stress profile questionnaires may be useful. A sample used is

attached (attachment 1)

.

Another factor, job dissatisfaction, may also contribute to the

occurrence of an accident. Any relationship between job dissatisfaction

and accidents is, however, unclear at this time. (Scott, 1972) Therefore,

no attempt to measure this factor was made.

The information collected in each case was evaluated to determine

if any characteristics of the worker, the tool, the task or work practices

contributed to the occurrence of each accident. Since the purpose of this

study was to develop a reporting system and involves a small data base;

no specific recommendations for reducing hand tool injuries were made.

With the previously discussed information requirements in mind, a

report form and procedure were developed incorporating the most advantageous

combination and sequence of activities. The form (attachment 2) is

standardized and includes a list of instructions. Further breakdown and

standardization may be needed to collect more. The form was used in a pilot

study at Tinker Air Force Base.

In this Pilot study the procedure followed was:

1. Location of subject

2. Completion of forms

3. Administration of the One Hole Test

8?
Data were collected in cooperation with the Tinker Air Force Base

Safety Office. All workers involved were employed by the Air Force

Logistics Command which in 1974 reported 13.5 percent of its work related

accidents to be associated with hand tools

.

The initial data were collected over a period of two days. First, all

accidents which occurred in June 1975 were surveyed and thirteen cases

involving handtools were extracted from the files . After consulting with

supervisors a week in advance, it was found that ten of the thirteen

would be available for consultation.

The information collected in each case was evaluated to determine that

characteristics of the worker, the tool, the task or work practices

contributed to the occurrence of each accident. With the previously

discussed information recpairemients in mind, the complete processing of each

subject required approximately ninety minutes; thirty minutes for

information collection and the rest for travel and subject location time.

Results and Discussion

Information collected from the initial ten subjects revealed the

following:

More specifically. Table 9 shows the predominance of manual tools and

finger injuries in the group of accidents surveyed.

This is, of course, too little information to identify any trends but

is sufficient to demonstrate that such details, descriptive of the injury

population, may easily be collected incidental to investigation for

cause. It is felt that the body of information collected did in fact

prove adequate to describe all of the accidents in terms of the system

characteristics . Table 10 summarized the system characteristics which

were identified as contributing factors in the causes of the initial ten

accidents

.

A validation of the effectiveness of the collected information was

accomplished by selecting five additional accident cases and investigating

them. Again all of the cases were easily described in terms of the system

characteristics involved. The data allowed an independent expert to

judge that he had a good understanding of each accident after reading

the reports.

Sex

Average age

Training

9 males , 1 female

36 years

2 subjects were trained to use

Average experience

Average time missed

due to injury

the tool involved

10.9 years

85.5 minutes

88
TABLE 9

SOURCE OF INJURY MID BODY PART INJURED FOR TEN CASES

AT TINKER AIR FORCE BASE

Body Part

Tool

Head Hand

Finger

Arm

elec. drill 1 1 1

elec. saw 1

wrerich 1 1

saw 1

pliers 1

file 1

razor blade 1

89
The information collected for the five additional accident cases

showed significant similarity to the results in the initial effort.

Table 11 summarized the data in terms of the system characteristics

.

Tables 10 and 11 suggest several interesting trends and conclusions which

will be discussed later in the Discussion and Conclusion section. While the

amount of data are too small to be conclusive and no scores for the whole

worker population are available, it appears that the One Hole Test may

be useful in pinpointing a deficiency in motor skill level. Certainly

it will be important to investigate motor skill as a system characteristic.

The results of the life stress profile were difficult to interpret.

Although there are no population norms to compare to, the finding suggests

a tendency toward risk taking behavior. How much this would account for

the common disregard of safe work practices is uncertain since many

additional factors must be considered such as simple overconfidence,

supervisor pressure to increase productivity, and ignorance of safety

rules etc.

Having established information requirements and shown the system

characteristics approach to be a reasonable method to describe an

accident for the purpose of analysis ; it remains to be decided how control

measures can be developed. After a major data collection effort, the

data will likely point to some obvious controls such as use of gloves

with certain tools or wider use of safety glasses , but in many cases

only the problems will be identified leaving the necessity of further

research to eliminate the hazard.

Discussion and Conclusions

Discussion

Tables 10 and 11 summarized the results of the accident investigations

in terms of the system characteristics which were principally involved in

each incident. Referring to these tables again, it is apparent that

certain of the characteristics are more common in occurrence than others.

While this sample is too small to be conclusive; individual work practices

clearly dominates while training and tool design and function show only

slightly less involvement and all three are highly related. Nfotor

skill, because of the One Hole Test score indications, is also a very

inportant characteristic.

On the basis of the information available from this study it is

suggested that the following be slated for primary emphasis in the initial

stages of any research which will follow:

Other system characteristics should be added to this list as progress is

made and additional funds and opportunities become available.

1.

2.

3.

4.

Individual Work Practices

Motor Skills

Training

Tool Design and Function

90
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92
This relatively small priority list matches the top two priorities

arrived at by Ayoub, Purswell and Hoag (1975) and includes training which

developed as the fifth priority in that study. Of course, the sample here

is too small to be conclusive but this does indicate that a degree of

confidence may be placed in the expert opinion method of priority

assignment developed by Ayoub et. al. (1975).

Conclus ion

Handtools are a serious threat to the worker who uses them when a

characteristic of himself, the tool, the task, work practices and/or their

interactions interferes with a safe application. The data available support

this statement since it shows that handtools account for between five and

10 percent of all work injuries. However, little can be done to improve

the safety of handtool use until more is known about what causes the

accidents which occur. A typical accident data collection form assigns

causes of accidents to categories . One form in particular uses the

categories listed below.

If carefully con^leted, these categories might reveal areas where emphasis

is needed to reduce injuries but the action taken could not be directed to

the cause because no specific cause is defined. There is, then, a void between

what causes accidents and what can be done to prevent them. To fill this

void a wide range of information is required; identifying the principal

causes of handtool accidents.

By incorporating the system characteristics of Purswell, Ayoub, and

Hoag into a data collection form it was shown that actual causes of accidents

can be identified. Once the syston characteristics identified most

frequently as principal causes are located, specific research can be needed

or preventive measures can be started in these areas . The research will

ultimately reveal the steps necessary to devise effective control measures

for handtool injuries.

1.

2.

3.

4.

5.

Unsafe Condition

Unsafe Act

IMsafe Personal Factor

Material Failure

No Fault of Personnel or Material

93
BIBLIOGRAPHY

1. Ayoub, M.M. , and McDaniel, Joe W. "Criteria and Standards for NonElectric Hand Tools; A Literature Review and Recommendations,"

report submitted to IMEW/PHS, National Institution for

Occupational Safety and Health, 1973.

2. Ayoub, M.M. , Purswell, J.L., and Hoag, Laveme "Research Requirements

on Hand Tools," report submitted to DHEW/PHS, National

Institute for Occupational Safety and Health, 1975.

3. Chevron Shipping Company, "Choose and Use Handtools Carefully,"

Safety Review , November 1970, 27 (11), 15.

4. National Safety Council Accident Facts . 1972 Edition, Chicago, Illinois

5. National Safety Council Accident Facts . 1973 Edition, Chicago, Illinois

6. National Safety Council Accident Facts . 1974 Edition, Chicago, Illinois

7. New York State Department of Labor. "Characteristics and Costs of

Work Injuries in New York State, 1966-1970," 1972, Vol. 1-10,

Special Bulletin, p. 243.

8. Salvendy, Gavriel "Selection of Industrial Operators, The One Hole

Test," Int. Journal Production Research, 1975, 13 (3), 303-321.

9. Scott, W.G., and Mitchell, T.R. Organization Theory a Structural and

Behavioral Analysis . Ontario : Irwin Dorsey Limited, 1972.

10. State of California, Department of Industrial Relations, Division of

Labor Statistics and Research. California Work Injuries- -1970,

San Francisco, March 1970, p. 36-37.

11. State of California, California Work Injuries , 1967-1972, Division of

Labor Statistics and Research.

12. The Industrial Commission of Ohio, Division of Safety and Hygiene,

Hand Tools , No. 4, 1967, p. 1-19.

13. Welford, A.T. Aging and Human Skill , A report centered on work by the

Nuffield Unit for research in problems of aging, Oxford

University Press, 1958.

94
ATTACHMENT 1

LIFE STRESS PROFILE

95

Attachment 1 - Life Stress Profile

(all responses are confidential)

(1) Do you generally eat at the same times each day?

Did you do so on the day of the accident?

(2) Were you planning special recreational activity for after work

the day of the accident?

(3) Were you concerned about a personal problem on the day of the

accident?

(4) Had you been off work for a full day or more prior to the day

of the accident, (including weekends)?

(5) On the day of the accident were you concerned about an important

financial or business arrangement?

(e.g., buying land, a car, insurance, etc.)

(6) Do you occasionally bet on football or play poker?

(7) On the average, how many alcoholic drinks do you drink in a

week? a day? (one can or glass equals one drink)

(8) On the day of the accident, did you have a disagreement with your

supervisor or a fellow worker?

(9) Was there a change in your working conditions within three days

prior to the accident?

97
How many work related accidents have you had in the last 12 months

including lost time, first aid and unreported accidents?

Prior to the accident were you engaged in any unusual off- the -job

activity? (e.g., overhauling a car, building a swimming pool,

etc.)

98
ATTACHMENT 2

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101
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Case ivuLaber 9 A'<^e OjXU oLitTLlCt: Xli ULlio clQQ ioiLIUXtiL jODS l^UlO ) lo Sex

Training for this tool? 11 Grade

i

1

Description of injury Injury tyoe Time of iniury

Body part L3 Minutes since break

Severity 14 Minutes to break

5 Work tim6 missed (minutes) L5 Hand used

7 Health ; Is it related to acc? Draw stick figures showing position

at the time of the accident and

describe the position of the hands

!

8 Below, trace the hand used

i

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102
r

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^

-/

/ Tool used

iS Function

19 Power class

20 List any protective equipment used

21 Were any holders, retainers, pouches. etc. , used?

22

If 21 is yes, describe:

1

i

!

1

Size, shape and balance

24 Texture: Causative?

25 Material:

\^ Cl UJ d l_ V W >

26 Weight

:

Causative?

27 Workplace:

Causative? E

28

i

1lV'orkpiece

:

1

t

1 Causative?

-4

29

! 30

Enviro nmen t

:

Causative?

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j Task Raquircnents

:

? Causative?

1

31

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j Individual work practices:

1 Causative?

!32

I CoTipaiiy work practices: Causative?

-

33 Government work practices: Causative?

3^:

1 Possible causes:

Causative?

, J35 j Co'aiments

:

i Causative?

103

SIMJIATION IN ACCIDENT RESEARCH

Stanley Rubinsky, Ph.D., P.E.

University of Rhode Island

STANLEY RUBINSKY is professor of industrial

engineering at the University of Rhode Island.

His research includes small power tool accident

research, study of hazards aboard commercial fishing

vessels, and the design of a state p].an for

implementation of OSHA in Rhode Island.

Rubinsky 's paper describes the use of two

types of simulators: (1) the "process simulator"

which is designed to perform like a normal machine

except that "an accident involving the simulator

cannot result in injury..."; and (2) the "accident

simulator" with which noninjurious "accidents" can

be caused to occur. The major difference between

these two types of simulators appears to lie in

the purposes of the experimental situations in which

they are employed. The process simulator was used in

studies to determine the variables affecting the

occurrence of accidents. The accident simulator was

employed to subject participants to "accidents" in

a training situation.

A classification of accidents by cause should be of help in developing

preventative measures . Such a classification scheme could include accidents

due to design deficiencies, accidents caused by negligent misuse, and those

caused by misuse or improper use because of lack of knowledge. Obviously,

accidents caused by design deficiencies would be eliminated by improving

the design. An example of this is a household electric meat grinder in

which an operator lost the tips of two fingers in the feed screw section.

Increasing the length of the entrance tube so that the fingers would no

longer reach the feed screw would eliminate the possibility of an accident

from this source. Accidents caused by deliberate negligence or misuse

are much more difficult to cope with. An investigation of the reasons

for the negligence would seem to be in order. Was the negligence the result

of fatique, drugs, mental stress, or a lack of appreciation for the possible

injury? Knowledge of these factors could suggest some program of remedial

action. If the accident were the result of the lack of knowledge or training,

the remedial steps are immediately apparent. But, what is the most effective

educational or training method? It was the attempt to answer some of these

questions which led to the investigation of simulation as a possible

research tool.

Incidentally, I am referring only to accidents and not to injuries

because, to my mind, they are essentially equivalent. It is usually pure

chance which separates the accident from which no damage occurs from that

in which substantial injury or even death could result.

10$
Our investigation into the causes o£ accidents led to the development

o£ two types of sijnulators . The first type, which we call the process

simulator, is designed to perform like a regular process, machine, or hand

tool except that an accident involving the simulator cannot result in injury

to the operator. For instance, the meat grinder could have been fitted

with a soft plastic or rubber feed screw and a soft substance such

as gelatine cubes substituted for the meat. Thus all possible methods

of misusing the grinder could be investigated and fingers caught in the

feed screw as a result of this misuse would not be injured. It was on this

basis that a punch press process simulator was designed and tested.

The Process Simulator

A Powermaster Benchmaster No. 142E 2-ton power driven bench press was

purchased and modified for use as a simulator. This press could be

operated in three ways: by foot pedal, by a hand lever, or by

a pair of interlocked handlevers , thus providing the option of operation in

any one of three modes, varying from no protection of the operator's hand

to protection of one or both hands

.

A typical accident with this machine occurs during a press cycle when the

operator fails to remove his hand from between the closing dies. The result

can vary from laceration of a finger tip to the complete loss of several

fingers. In order to eliminate the possibility of real injury to the operator,

a modification of the blanking or stamping die normally mounted in the

machine was made. The lower, or female, half of the die pair was made in the

usual form, except that it was fabricated of wood and painted to resemble

metal. The male, or upper half of the pair, however, was made of Porlon, a

plastic material containing micropores filled with ink. The modified die

is, in effect, a self- inking rubber stamp. This die substitutes an inked

inipression from a soft die for the stamped impression made by a steel die.

The Porlon "die" was fastened to a spring -mounted dieholder so that when

an operator's finger was caught between the pair of dies no injury, pain,

or discomfort would result. The operator did suffer an inked mark on the

"injured" finger. Heavy card stock was substituted for the metal blanks

normally used as wor]q)ieces.

The press was also equipped with a counter to register the number of

strokes of the press , and with a second counter actuated by a microswitch

mounted on the spring dieholder to accumulate a count of "accidents." A

light and a buzzer were connected to the circuit that was counting the

accidents. Suitable switches made it possible for the buzzer to be

disconnected. The counting circuit thus could be used selectively to

signal the operator when an error or accident occurred.

The simulator was tested, first to determine whether accidents

could be forced to a reasonably high and countable frequency and, second,

to ascertain whether those variables which were thought to influence

real accidents would similarly influence the frequency of simulated accidents.

106
The punch press was set up to stamp cards using the foot pedal control

mode. Thus, since there were no guards on the press either or both hands

could be caught between the dies . Twenty college students , 10 male and 10

female, volunteered to serve as subjects. The males were divided randomly

into two groups , as were the females . One group of males and one of females

were paid a flat hourly rate. The second set of groups were paid the same

hourly rate as a minimum, but could earn more money by increasing their

output. Both groups were instructed in the designated method of operation

and each subject was allowed an eight-minute practice period and a twominute rest before the production run. The subjects were told that the

experiment was designed to study the effect of workplace layout and design

on production output.

The test results revealed that six of the twenty subjects were accident

free and that two of the subjects incurred six accidents each during a onehour run. An analysis of the results led to the conclusion that accidents

could be made to occur with sufficient frequency to allow a meaningful study

in a reasonable length of time and, further, that the frequency of accidents

could be manipulated by changing experimental conditions

.

Following this work, the simulator was refined by replacing the

lower die block by an aluminum block in which were embedded four sensors

,

one in each corner, which enabled the experimenter to determine that a

workpiece was in place at each stroke of the press and also that the

workpiece was properly positioned so as to produce a good part. Further, a

delay circuit was introduced so that an accident shut off power to the press

for a predetermined time in order to introduce a money penalty. In addition,

the press has been equipped with a vigilance task. At the appearance of a red

light, the operator is required to push a button to extinguish the light

before operating the next press cycle. Failure to activate the button results

in a press shut down of a shorter duration than that of the accident shut down.

Also, all the counters and control equipment are now located at a remote

location so that the observer is not in the same room as the subject and

can, therefore, have no effect on the subject's performance. Additional

research using this simulator is now going on.

The Accident Simulator

The second type of simulator is that which simulates the accident, again,

with no danger to the operator. In the design of this device, several

criteria were set up. First, the "injury" resulting from the accident should

be aversive to the subject; second, the "injury" must be directly related to

the accident; third,' the unsafe act causing the accident should not be

trivial; fourth, the total environment should be realistic; and fifth, the

injury must be certifiable by an objective and competent jury as being

physically and psychologically harmless to the subject.

A bench grinder was modified and equipped with water jets that could

be used to spray the operator (an aversive stimulus) in such a way as to

simulate an exploding grinding wheel or a flying spark. Originally, the jet

was activated by a hidden remote switch controlled by the experimenter.

107
Since the unsafe act consisted o£ standing in front of the grinder during

the start up period, the manual switch was replaced by a hidden mat switch

located in front of the grinder. If the operator started the machine while

standing on the mat, the spray was activated. If the operator stepped in

front of the grinder after it reached operating speed, the spray was not

activated.

The accident simulator was used to investigate its effectiveness as

an aid in safety training and education. Basically, two questions were

explored. First, did the demonstration of an accident aid in the training

for the safe use of a machine and, second, was there any additional value in

having the trainee actually experience the simulated accident?

Briefly, thirty-two subjects were randomly divided into four groups.

Each group received written instructions and a demonstration of the correct

method of operating the grinder. In addition, one group received a

demonstration of the simulated accident, another group was subjected to the

accident while operating the grinder, and the last group received both a

demonstration and an experience of the accident. In all cases, the simulated

accident was used only during the orientation session and never used during

the test sessions. All subjects were told that the object of the experiment

was to test their ability to separate 10 samples of steel by observing the

pattern of grinding sparks. Each subject, therefore, started the machine

ten times. An analysis of the results of this first experiment showed that

all three groups exposed to the simulated accident either by demonstration,

by experience, or both, had statistically significantly fewer accidents

than the members of the one group that had no experience with the simulated

accident. There were no significant differences among the other groups.

A second test involving 72 college students was arranged to duplicate

the first experiment except that each subject was tested three times with

a one week interval between tests one and two, followed by a three week

interval between tests two and three. The result of this experiment showed

that while the mean number of accidents of all groups seoned to be reduced

somewhat with the passage of time, the differences were not significant except

that the group for which the accident was both demonstrated and experienced

had significantly fewer accidents than did the other groups

.

A third test involving 120 volunteer students was conducted. In this

test the control group of 30 students received written instructions and a

demonstration of the correct procedures , as had been done in the two previous

experiments. The remaining three groups were each shown and subjected to

training accidents, one group to two, a second to five, and the remaining

group to ten accidents. In addition, each group was subdivided and one

subgroup was given a consecutive schedule of accident exposure and the

other an intermittent randomly selected schedule of exposures. Finally,

the groups were all tested for retention of training at one month, three

month, and six month intervals.

By the end of six months, 80 subjects remained so the groups were

equalized by randomly eliminating subjects from the larger groups. The

analysis of the results surprised us. Briefly, the difference of all

108
groups from the control group exceeded expectations , but there was no

significant difference among any of the other groups nor was there a difference

between subgroups attributable to differing schedules of accident exposure.

Finally, it was clearly shown that the improvement in the accident rate

which was attributed to use of the simulator was retained for at least six

months after training.

Thus, we believe that accident simulation offers a powerful means for

training in safety procedures. However, this is not necessarily an easy undertaking since the simulation should meet the criteria already stated. One

may conceive, for instance, of arranging for accidents in a driving simulator

but it is doubtful that such accidents would have much effect on subsequent

driving habits unless and until a suitable aversive result of the accident

can be devised.

Process simulation requires only that it be realistic in its operation

and conpletely harmless to the operator. The present punch press simulator

is now being used to study effects of secondary tasks. It may be used to

study machine guarding; the effect of fatigue, drugs, visual and aural distraction, noise; and other such factors and their effect on a machine operator.

To sum i:^, we believe that both types of simulators will prove to be

valuable learning and research tools in our efforts to gain a better insight

into the causes and prevention of accidents.

109
1

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Participants

Jonathan Adler

National Bureau of Standards

Washington, D.C.

* M. M. Ayoub

Texas Tech University

Lubbock, Texas

* Ludwig Benner, Jr.

National Transportation Safety

Board

Washington, D.C.

** Philippe V. Garden

National Institutes of Health

Bethesda, Maryland

Robert Cunitz

National Bureau of Standards

Washington, D.C.

* Robert Eicher

Energy Research and Development

Administrat ion

Washington, D.C.

John V. Fechter

National Bureau of Standards

Washington, D.C.

Charles Fried

National Bureau of Standards

Washington, D.C.

* Willie Hammer

Hughes Aircraft Company

Culver City, California

Clarke E. Jones

National Bureau of Standards

Washington, D.C.

Joel Kramer

National Bureau of Standards

Washington, D.C.

* Invited Presentation

** Dinner Speaker

Pat Meguire

National Bureau of Standards

Washington, D.C.

J. J. Persensky

National Bureau of Standards

Washington, D.C.

* George A. Peters

Los Angeles , California

Val Pezoldt

National Bureau of Standards

Washington, D.C.

R. David Pittle

Consumer Product Safety Commission

Washington, D.C.

Louis G. Porter

National Bureau of Standards

Washington, D.C.

Jerry Purswell

University of Oklahoma

Norman, Oklahoma

Jerry Ramsey

Consumer Product Safety Commission

Washington, D.C.

Stuart Robinson

National Bureau of Standards

Washington, D.C.

* Stanley Rubinsky

University of Rhode Island

Kingston, Rhode Island

* Rose E. Steidl

Cornell University

Ithaca, New York

Harold P. Van Cott

National Bureau of Standards

Washington, D.C.

* Julian A. Waller

IMiversity of Vermont

Burlington, Vermont

i- U. S. GOVERNMENT PRINTING OFFICE : 1977--240-848/214 111
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBS SP-482

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE , Rare Event/Accident Research Methodology

Proceedings of a Workshop held at the National Bureau of

Standards, Gaithersburg, Maryland, May 26-28, 1976

5. Publication Date Julv 1977

6. Performing Organization Code

7. AUTHOR(S)

V- J- Pezoldt- Editor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 441-0126

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as item 9

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Libraiy of Congress Catalog Card Number: 77-608110

16. ABSTRACT (A 200-word or less {actual summary ot most sigpilicant information. II document includes a signilicant

bibliography or literature survey, mentiai it here.)

This volume contains the formal papers presented at a Workshop on Rare

Event/Accident Research Methodology sponsored by the Human Factors Section of

the Center for Consumer Product Technology, National Bureau of Standards

held at NBS May 26-28, 1976. The topics addressed at the workshop and

reflected in the papers in this volume include system safety engineering,

hypothesis generation in accident research, epidemiological approaches to

injuiy research, observational techniques for studying complex tasks, accident

sinailation, and methodological considerations being forced by the law.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only tfie lirst letter of the first key word unless a proper name; separated by semicolons)

Accident research; human factors; methodology; rare events; safety; system safety

18. AVAILABILITY [X] Unlimited

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BIBLIOGRAPHIC SUBSCRIPTION SERVICES

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Cryogenic Data Center Current Awareness Service. A

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Superconducting Devices and Materials. A literature

survey issued quarterly. Annual subscription: $30.00 . Send subscription orders and remittances for the preceding bibliographic services to National Bureau of

Standards, Cryogenic Data Center (275.02) Boulder,

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